UI: PiP Button Component

[mihar-22]

Implement the PiPButton component for toggling picture-in-picture mode. Includes core interaction logic, DOM props builder, and React/HTML implementations.

Supports both document PiP (container target, custom controls visible) and video PiP (media target, native PiP window).

References

• Vidstack: PIP Button
• Media Chrome: PiP Button
• Document Picture-in-Picture API (MDN)