Add web UI, AGPL3, notifications, continue watching, bulk watched, storage stats, scheduler

License:
- GPL3 → AGPL3

New features:
- Web interface (--web [port]): axum/tokio server with SSE progress, library browser,
  download trigger, watched toggle; embedded single-page HTML/JS UI
- Desktop notifications via notify-rust when downloads complete or fail
- Continue Watching sidebar entry showing videos with saved resume positions
- Bulk select mode: select multiple videos, mark all watched/unwatched at once
- Storage stats: channel disk usage shown in sidebar next to video count
- Scheduled channel checks: configurable interval (hours), auto re-downloads all
  tracked channels using channel_url from info.json; enabled in Settings

Theme fixes:
- Scene Queen: remove override_text_color so active button text uses fg_stroke
  (dark navy on neon green) instead of near-white — fixes unreadable contrast
- Trans: override_text_color → hot pink #cc0066 for pink-tinted text throughout

Settings additions:
- Auto-check channels toggle + interval_hours DragValue
- Web UI port setting

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Cargo.toml

@@ -12,6 +12,11 @@ serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 rusqlite = { version = "0.31", features = ["bundled"] }
 tray-icon = "0.13"
+notify-rust = { version = "4", default-features = false, features = ["d"] }
+axum = { version = "0.7", features = ["macros"] }
+tokio = { version = "1", features = ["full"] }
+tokio-stream = { version = "0.1", features = ["sync"] }
+tower-http = { version = "0.5", features = ["cors"] }
 
 [profile.release]
 opt-level = 2