feat(electrobun): wire EVERYTHING — all settings persist, theme editor, marketplace

All settings wired to SQLite persistence:
- AgentSettings: shell, CWD, permissions, providers (JSON blob)
- SecuritySettings: branch policies (JSON array)
- ProjectSettings: per-project via setProject RPC
- OrchestrationSettings: wake, anchors, notifications
- AdvancedSettings: logging, OTLP, plugins, import/export JSON

Theme Editor:
- 26 color pickers (14 Accents + 12 Neutrals)
- Live CSS var preview as you pick colors
- Save custom theme to SQLite, cancel reverts
- Import/export theme as JSON
- Custom themes in dropdown with delete button

Extensions Marketplace:
- 8-plugin demo catalog (Browse/Installed tabs)
- Search/filter by name or tag
- Install/uninstall with SQLite persistence
- Plugin cards with emoji icons, tags, version

Terminal font hot-swap:
- fontStore.onTermFontChange() → xterm.js options update + fitAddon.fit()
- Resize notification to PTY daemon after font change

All 7 settings categories functional. Every control persists and takes effect.

ui-electrobun/src/bun/settings-db.ts

@@ -162,6 +162,10 @@ export class SettingsDb {
       .run(id, name, json);
   }
 
+  deleteCustomTheme(id: string): void {
+    this.db.query("DELETE FROM custom_themes WHERE id = ?").run(id);
+  }
+
   // ── Lifecycle ─────────────────────────────────────────────────────────────
 
   close(): void {