Rename from TutorialDock to TutorialVault. Remove legacy Python app
and scripts. Fix video playback, subtitles, metadata display, window
state persistence, and auto-download of ffmpeg/ffprobe on first run.
Bundle fonts via npm instead of runtime download.
- video_protocol.rs: tutdock:// custom protocol with HTTP Range support
for video streaming, subtitle/font serving with path traversal protection
- commands.rs: all 26 Tauri command handlers as thin wrappers
- main.rs: full Tauri bootstrap with state management, window restore,
async font caching, and ffmpeg discovery
- index.html: complete HTML markup extracted from Python app
- lib.rs: updated with all module declarations and AppPaths struct
