feat(plugins): add JavaScript plugin system with overlay panel

- Load plugins from <config dir>/plugins/<id>/ when enabled under `plugins` in config
- Expose ctx with mpv events/commands, timers, subtitle context, actions, notify, exec, and panel
- Bind plugin actions via `__plugin-action:<id>/<action>` keybindings (runPluginAction session action)
- Add plugin-panel modal with markdown rendering; closing aborts the panel signal
- Add ai-explain example plugin that queries `codex exec` for the current line
- Add e2e harness `files` option and plugin e2e scenario; document plugins in docs-site and internal docs

src/config/resolve.ts

@@ -4,6 +4,7 @@ import { createResolveContext } from './resolve/context';
 import { applyCoreDomainConfig } from './resolve/core-domains';
 import { applyImmersionTrackingConfig } from './resolve/immersion-tracking';
 import { applyIntegrationConfig } from './resolve/integrations';
+import { applyPluginsConfig } from './resolve/plugins';
 import { applyStatsConfig } from './resolve/stats';
 import { applySubtitleDomainConfig } from './resolve/subtitle-domains';
 import { applyTopLevelConfig } from './resolve/top-level';
@@ -15,6 +16,7 @@ const APPLY_RESOLVE_STEPS = [
   applyIntegrationConfig,
   applyImmersionTrackingConfig,
   applyStatsConfig,
+  applyPluginsConfig,
   applyAnkiConnectResolution,
 ] as const;