In `library`, add component `skeleton`

As a user of the Ouds library
I want to be able to use the component
So that I can add this Ouds component in my own projects

As a user of the library
I want to be able to use the component
So that I have access to the documentation on how to use it

As a user of the Demo App
I want to access the Component
So that I can understand how to use it:

while using the demo app I can interact with the available options and observe the changes on the component itself
I can see the code associated to the component customization
I can copy and paste the code from the app based on the selected customization
or when looking into the code of the app itself, I would also understand how to use it

Need to update Figma with these specifications coming from dev/design meeting (10.09.2026):
- Shimmer effect must be applied on whole screen from left to right on mobile.
- All shapes must be allowed

Add component skeleton (API, doc, demo app) with shimmer effect and circle shape
Add component skeleton (API, doc, demo app) with shimmer effect and capsule shape
Add component skeleton (API, doc, demo app) with shimmer effect and rectangle shape with square corners
Add component skeleton (API, doc, demo app) with shimmer effect and rectangle shape with rounded corners
Add component skeleton (API, doc, demo app) with shimmer effect and square shape
Add snapshots tests for skeleton

Description