feat: improve inline video player UX

[barrydeen]

Summary

• Dynamic aspect ratio — detects actual video dimensions instead of hardcoded 16:9, with 500dp max height cap for portrait videos
• Autoplay/autopause — videos auto-play when >50% visible and pause when scrolled out of view
• Controls on tap — native ExoPlayer scrubber and play/pause hidden by default, revealed on tap with 2s auto-hide. Mute and fullscreen buttons overlay in sync
• Global mute — videos start muted; toggling unmute on any video unmutes all videos for the session
• User pause respected — tapping pause won't be overridden by visibility autoplay; resets when scrolled away and back
• RESIZE_MODE_ZOOM — eliminates black bars around videos by filling the container

Test plan

• Verify landscape videos render full-width without black bars
• Verify portrait/vertical videos render at correct proportions (not squished), capped at reasonable height
• Scroll videos in and out of view — confirm autoplay/autopause
• Tap pause, confirm video stays paused while in viewport
• Scroll paused video out and back — confirm it resumes
• Tap video to show controls, confirm scrubber/play-pause/timeline appear and auto-hide after ~2s
• Tap mute button on one video, scroll to another — confirm it's also unmuted
• Restart app — confirm videos default to muted again
• Tap fullscreen — confirm it opens full screen player at correct position