Add embedded egui-video player with fullscreen support

[alltheseas]

PR Summary

Embedded egui-video now powers inline MP4 playback in notes: videos download/cached off-thread, auto-start with audio, allow pause/resume toggles by
tapping the frame, and offer a fullscreen overlay (no extra window, ESC/✕ to exit). The shared SDL device keeps audio in sync.

builds on https://github.com/bu5hm4nn/egui-video-rs

testing

Tested on Linux machine only

[alltheseas]

android plan

1. decode with android native MediaCodec
2. from rust drive MediaCodec via JNI calls
3. present frames in egui/wgpu without copies
4. create Android only VideoPlayerAndroid that mirrors desktop API (with_audio, ui, etc) that internally commands the codec service

[alltheseas]

android plan

1. decode with android native MediaCodec
2. from rust drive MediaCodec via JNI calls
3. present frames in egui/wgpu without copies
4. create Android only VideoPlayerAndroid that mirrors desktop API (with_audio, ui, etc) that internally commands the codec service

draft Android MediaCodec commit b68d815

testing

Untested