fix: improve PiP player controls and rendering

[barrydeen]

Summary

• Add play/pause toggle to PiP overlay with tap-to-reveal controls (auto-hide after 2s)
• Suppress feed video auto-play while PiP is active to prevent interference
• Wire up missing fullscreen callback on livestream player
• Replace PlayerView (SurfaceView) with TextureView in PiP to fix z-ordering bleed-through from inline videos

Test plan

• Put a video in PiP, verify controls are hidden by default
• Tap PiP to reveal play/pause, fullscreen, close — verify they auto-hide after 2s
• Scroll feed while PiP is active — verify no other video content bleeds into PiP
• Verify feed videos do not auto-play while PiP is active
• Open a livestream, tap fullscreen — verify it opens the fullscreen player