feat(plugins): add Anki card-mined event, AnkiConnect invoke, anki-sync

- Add ctx.anki.on('card-mined') fed by polling, proxy, and card creation once enrichment finishes
- Add ctx.anki.invoke to send one AnkiConnect action to the effective url with no retries
- Ship example anki-sync plugin that syncs to AnkiWeb after mining goes quiet or playback ends
- Unload plugins that finish activating after unloadAll gave up on them
- Document the Anki API and anki-sync plugin in docs-site and architecture docs

changes/plugin-system.md

@@ -1,5 +1,6 @@
 type: added
 area: plugins
 
-- Added JavaScript plugins loaded at startup from `<config dir>/plugins/<id>/` and enabled under `plugins` in the config. Plugins can listen to mpv events, run timers, register actions bound with `__plugin-action:<id>/<action>` keybindings or run with `--plugin-action`, run built-in actions, start mpv, run programs, keep state in a per-plugin data folder, and show results in an overlay panel or their own window.
+- Added JavaScript plugins loaded at startup from `<config dir>/plugins/<id>/` and enabled under `plugins` in the config. Plugins can listen to mpv events, run timers, register actions bound with `__plugin-action:<id>/<action>` keybindings or run with `--plugin-action`, run built-in actions, react to mined Anki cards and call AnkiConnect, start mpv, run programs, keep state in a per-plugin data folder, and show results in an overlay panel or their own window.
 - Added an example `ai-explain` plugin that sends the current line and its neighbors to `codex exec` and shows a translation or grammar explanation.
+- Added an example `anki-sync` plugin that syncs Anki to AnkiWeb after you mine cards, once mining goes quiet or playback ends.