We're not shapeshifting, which is cool
But you're also asking for a hard-science evolution-oriented justification for a fantasy animal — which isn't as cool. Evolution usually chooses the simplest change that favors continued survival. The really complex aspects of humanity (eyesight, our brain...) are the result of a long series of simple changes, each overcoming a disadvantage and promoting continued survival.
Werewolves will never meet that basic criteria. They're too complex for too little benefit (if any). To really meet your hard-science expectation, we would also need to address disease and healing — both of which will be massive disadvantages for a creature as complex as a werewolf. How, for example, would the human-form aspect deal with a disease that's afflicting the wolf-form and vice-versa? The illness wouldn't simply go away with the change. What happens if the human-form werewolf is playing soccer and tears one of the tendons I advocate for the second ankle? The more complex something is without a justifying benefit, the less likely it can be rationalized evolutionarily because it breaks (and therefore is eaten) too easily.
Consequently, my answer will focus only on real-world physiology that can be used to explain how a hard-science werewolf would behave.
1. Facial Appearance
Honestly, you made this a LOT simpler by only focusing on appearance. Shifting bone plates around would be no small thing and incredibly hard to justify from an evolutionary standpoint. They'd always represent an exploitable weakness without a compensating strength. But appearance can be explained using the same basic mechanisms as a male erection.
An erection results from a complex interaction of neurologic, vascular, hormonal, and psychologic stimuli. Pleasurable stimuli cause the brain to send nerve signals through the spinal cord to the penis. The arteries supplying blood to the erectile tissue (the corpora cavernosa and corpus spongiosum—see figure Male Reproductive Organs) respond by widening (dilating). The widened arteries dramatically increase blood flow to these erectile areas. At the same time, muscles around the veins that normally drain blood from the penis tighten, slowing the outflow of blood and elevating blood pressure in the penis. This combination of increased inflow and decreased outflow is what causes the penis to become engorged with blood and increase in length, diameter, and stiffness. (Source)
I believe it's a small ignorance to allow the human face to remain soft, but reasonably rigid, perhaps like an overweight person's face. The change to a werewolf would simply require the (obviously not necessarily "pleasurable") stimulus to increase blood pressure to the previously collapsed snout. The action would also flatten the human nose in the process, resulting in a canine look. Obviously, it would be much simpler if your werewolf were based on a Pug or a Bulldog than a Doberman or a Shepherd.
The change to a tough, blackened canine proboscis is something I think you'll need to walk away from.
2. Teeth
This most sophisticated fang type evolved once, in the ancestor to all modern vipers, which lived in Asia about 40 million years ago. ... Solenoglyphous fangs are long and tubular and are attached to the snake's maxillary bone. (Source)
Your werewolf can utilize solenoglyphous teeth, meaning through bone and muscle structure, they lay down, perhaps in a fold of skin, and only rise when in "werewolf mode."
And this is why I appreciate that you're only looking for the face to change appearance. Changing the bone structure of the skull to reflect a wolf's mandible is, from a hard-science perspective, impossible.
3. Ears
Pointing the ears operates on the same premise as the snout, nose, and face. As for rotating the ears, humans already have the genetic flotsam to rationalize this.
Ear wiggling happens through muscles above and behind your ears called auriculars. In some animals, these muscles are useful because ear movement is helpful. A cat, for example, can move its ears to help it listen for tasty birds. But why would humans have these muscles? Way back when, humans and cats had the same ancestors. Ear wiggling was useful to this shared ancestor. (Source)
Your real problem, and you're stuck with it, is that you can't move the ears to the top of the skull. That would either require moving the holes/passages through the skull (and the channels inside the skull) or having stretchable channels between the ear and the skull such that muscles could pull them up. I simply don't like this idea. I think it's on the impossible side of believable, especially in a hard-science context. So, you have pointed ears and they can rotate, but they're on the side of the head.
4. The ankle
You've already solved this problem. There isn't a hard-science solution to making bone stretch and contract. Sorry. It's very purpose is to not stretch and contract. The only solution is a hidden, second ankle that is locked in place in human-form and released in werewolf-form.
This isn't that unbelievable. Birds do exactly what you require.
Two thin tendons, called flexor tendons, extend from the leg muscles down the back of the tarsus bone and attach to the toes. When a bird lands on a perch, these tendons tighten and so the toes lock around the perch. This involuntary reflex keeps a sleeping bird from falling off a perch. The tendons stay tight until the legs straighten. As the bird stands up, it jumps up, its legs straighten, the tendons relax and the toes unlock to release the feet. Falling asleep doesn’t change the grip, as the weight of the bird keeps the leg in the locked position. (Source)
Where birds don't have a lot (if any) of muscle in their legs and claws, I think it's reasonable that your werewolves do. The tendons run from the knee to the lower ankle. The hard part is rationalizing how they tighten. For a bird, it's mechanical. Their weight when they land automatically tightens the tendons. For your werewolves, a unique muscle connecting from bone to tendon would be required to cause the tendons to tighten.
5. Fingers and toes
This one's almost as tough as the ears and ankle. Bones can't stretch and contract or they don't do what you need them to do: act as the foundation of everything else on the body. It would be like building a house on Styrofoam rather than concrete.
But we have those fangs we mentioned in snakes, and we have the fictional character of the Wolverine. Frankly, this is the least believable solution I'm going to offer, because I can't find an example in nature of a bone that is extended (pushed) between two other bones to create an extended something. And yet that's what you need.
Think of holding a toothpick in a pair of tweezers, then imagine a muscle or combination of muscle and bone that would push that toothpick out and pull it back.
This is a MASSIVE WEAKNESS. Yes, I can imagine the physiology of the solution, even if you had to use a leveraging bone (like used for the fangs or similar to the ear drum assembly) to push the extending bone out. The problem is that this is incredibly weak and easy to break. We're talking about fingers.... From a hard-science perspective, I hate this particular recommendation and hope someone else can come up with a better solution — because I'd leave the fingers and toes unchanging over doing this. It's weakening the body for the purpose of aesthetics, and that's not evolutionary at all.
6. Flexible skin
So far I've not advocated anything that would require this, so I'm going to ignore it. If I was forced to not ignore it, I'd point out that skin is already malleable — it just normally takes months or years to stretch and contract as you desire.
7. Body hair
I was surprised to find some interesting facts about rapid hair growth.
“Eating a well-balanced diet with adequate protein intake is important for optimal hair growth,” she added. “Generally, we recommend 50 grams of protein or more per day.”
According to the study, caffeine may help promote new hair growth at the molecular, cellular, and organ levels in both men and women.
Specific vitamins, minerals, and fatty acids are especially important for your overall health and also play a key role in providing your body with the energy needed for hair growth.
And then there's my favorite...
“[Platelet-rich plasma] is a breakthrough treatment that uses injections of a concentration of a patient’s own platelets to restore and accelerate hair growth,” she said. “Platelets are protein derived from one’s own bloodstream and DNA that can act like a stem cell when placed back into the body,” (Source for all of the above)
Will any or all of that cause hair to grow 2cm in an hour? Nope. But I love the setup because werewolves would have a nutrient-rich and protein-rich diet and would need a souped-up version of adrenaline (oh, let's call it a naturally occurring caffeine). Add to this the idea of a much more dense capillary system at the hair follicles (leading the untanned werewolf to look like they were body-blushing all the time) to deliver all that protein, all those nutrients, and a steady supply of stem cells — and you have a fine, fluffy hair in no time.
As for getting rid of the hair when changing from wolf-to-human, you need only look into how animals shed. The feline brain triggers the shedding process based on the amount of natural sunlight. What's being triggered is the follicle pinching off the hair. Your werewolf does the same thing... it's just triggered (a bit of humor here) off the amount of moonlight.
8. The Tail
Ugh. The tail. I may hate this section as much as I hated fingers and toes. A tail is actually an extension of the spine. It's not like you can pull it in (e.g., #1) or fold it someplace (e.g., #2). Worse still, the hair isn't just 2 cm long. It's a lot longer. I may suddenly understand why so many modern movie and game werewolves are sans tail.
I can't think of any real-life animal that does anything other than let the tail be. If you search for "hiding the tail" you'll get a million search results relating to crochet, yarn, sewing, and thread.
I'd vote for going tailless. But if you insist, the only solution I can think of is to wrap the tail between the werewolve's legs and up the stomach when in human-form. You could consider that some lizards practice autotomy, the choice to break or amputate a tail as a defensive reaction, which then grows back. But justifying the growth of spinal column material in an hour is a hard row to hoe. But that's the best I can do.
Errata
If you were actually looking for a hard-science explanation of shape shifting into werewolf form — I don't believe that can be achieved. I can't even imagine a valid hard-science solution for modifying, growing, shrinking, or shifting around bones from the skull to the tail and legs. Frankly, the skeleton is your biggest problem. IMO, in a hard-science context, you can't modify the skeleton between states. Otherwise you're not hard-science anymore. But that's just my opinion. Hopefully someone will come up with something that will prove me wrong.
