feat(plugins): add versioned plugin API with media snapshots and provena

- Add standalone src/plugin-api.ts types and manifest apiVersion check
- Add ctx.media playback snapshots, ctx.signal, ctx.onDispose, and awaitable ctx.mpv.request
- Bound async activation; actions wait only for their own plugin
- card-mined now carries per-note provenance (media + subtitle captured at mining start) through merges and YouTube queues
- Port episode-tags and auto-jimaku to provenance and media snapshots; drop mining-goal docs

docs-site/websocket-texthooker-api.md

@@ -206,7 +206,7 @@ The same pattern works for n8n or Zapier workflows, Discord notifiers, or append
 
 ## mpv script messages
 
-SubMiner has no in-app plugin SDK. Besides the streams above, you can drive it from other mpv scripts and from the [launcher CLI](/launcher-script).
+SubMiner also supports [JavaScript app plugins](/plugins) for playback events, mining events, actions, and custom UI. Besides the streams above, you can drive it from other mpv scripts and from the [launcher CLI](/launcher-script).
 
 The mpv plugin accepts these script messages: