Phase 3: Plugin-UI-System (WordPress-Style)

Backend:
- PluginManifest um 5 neue UI-Felder erweitert: menu_items, page_routes,
  detail_tabs, settings_pages, dashboard_widgets (FrontendMenuItem,
  FrontendPageRoute, FrontendDetailTab, FrontendSettingsPage,
  FrontendDashboardWidget)
- GET /api/v1/plugins/active-manifests Endpoint liefert UI-Manifeste
  aller aktiven Plugins
- Registry.get_active_manifests() + PluginService.get_active_manifests()
- 12 Built-in Plugins mit UI-Manifest-Daten gefuellt (menu_items,
  page_routes, detail_tabs, settings_pages)
- Plugin-Install-System: POST /upload (ZIP), POST /install-url (URL)
  mit Validierung (Manifest, dangerous imports, SQL migrations)

Frontend:
- pluginStore.ts (Zustand) mit PluginUiManifest Typen + Selektoren
- useActivePluginManifests() React Query Hook
- PluginRegistry.tsx — fetcht Manifeste beim App-Start
- PluginLoader.tsx — dynamisches React.lazy() mit ErrorBoundary
- PluginRouteRenderer.tsx — Catch-all fuer Plugin-Routes
- routes/index.tsx — Catch-all Routes fuer Plugin-Pages + Settings
- Sidebar.tsx — dynamische Plugin Menu-Items mit Grouping + Icons
- Settings.tsx — dynamische Plugin Settings-Pages
- ContactDetail.tsx — dynamische Plugin Detail-Tabs mit Permissions
- AppShell.tsx — PluginRegistry Provider eingebunden
- SettingsPlugins.tsx — Install-UI (ZIP Upload + URL Install)
- plugins.ts — useUploadPlugin() + useInstallPluginFromUrl() Hooks

Docs & Templates:
- docs/plugin-development-guide.md — komplette Entwickler-Doku
- templates/plugin-template/ — Boilerplate mit allen Manifest-Feldern

Tests:
- 34 Vitest-Tests (PluginRegistry, PluginLoader, PluginRouteRenderer,
  pluginStore) — alle bestanden
- TSC: keine neuen Errors (nur pre-existing Dms.tsx)

templates/plugin-template/README.md

@@ -0,0 +1,60 @@
+# Plugin Template
+
+A minimal plugin template for LeoCRM. Copy this directory to `app/plugins/builtins/<your_plugin_name>/` and customize.
+
+## Quick Start
+
+1. **Copy the template:**
+   ```bash
+   cp -r templates/plugin-template app/plugins/builtins/my_plugin
+   ```
+
+2. **Rename the plugin class:**
+   Edit `plugin.py` and rename `ExamplePlugin` to your plugin name.
+
+3. **Update the manifest:**
+   - Change `name`, `version`, `display_name`, `description`
+   - Add your routes, events, migrations, permissions
+   - Add UI contributions (menu items, page routes, etc.)
+
+4. **Implement routes:**
+   Edit `routes.py` with your API endpoints.
+
+5. **Add database models:**
+   Uncomment and customize `models.py`.
+
+6. **Write migrations:**
+   Add SQL migration files to `migrations/`.
+
+7. **Write tests:**
+   Add tests to `tests/test_plugin.py`.
+
+## Directory Structure
+
+```
+templates/plugin-template/
+├── __init__.py          # Package init
+├── plugin.py            # Plugin class with manifest (required)
+├── routes.py            # FastAPI route definitions
+├── models.py            # SQLAlchemy models (optional, commented out)
+├── schemas.py           # Pydantic schemas (optional)
+├── services.py          # Business logic (optional)
+├── migrations/          # SQL migration files
+│   └── 0001_initial.sql
+├── tests/               # Plugin tests
+│   ├── __init__.py
+│   └── test_plugin.py
+└── README.md            # This file
+```
+
+## Manifest Fields
+
+See `docs/plugin-development-guide.md` for a complete reference of all manifest fields.
+
+## Key Points
+
+- All API routes must be secured with `require_permission`
+- Event handlers are named `on_<event_name>` with dots replaced by underscores
+- Migration files run in alphanumeric order
+- UI component paths use the `@/` alias (resolved to `src/` by Vite)
+- i18n keys should be prefixed with the plugin name