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/models.py

@@ -0,0 +1,38 @@
+"""
+SQLAlchemy models for the example plugin.
+
+Uncomment and customize for your plugin's data model.
+"""
+
+# from __future__ import annotations
+#
+# import uuid
+# from datetime import datetime
+#
+# from sqlalchemy import Boolean, Column, DateTime, ForeignKey, String, Text
+# from sqlalchemy.dialects.postgresql import UUID
+# from sqlalchemy.orm import Mapped, mapped_column, relationship
+#
+# from app.database import Base
+#
+#
+# class ExampleItem(Base):
+#     __tablename__ = "example_items"
+#
+#     id: Mapped[uuid.UUID] = mapped_column(
+#         UUID(as_uuid=True), primary_key=True, default=uuid.uuid4
+#     )
+#     tenant_id: Mapped[uuid.UUID] = mapped_column(
+#         UUID(as_uuid=True), ForeignKey("tenants.id"), nullable=False
+#     )
+#     name: Mapped[str] = mapped_column(String(200), nullable=False)
+#     description: Mapped[str | None] = mapped_column(Text, nullable=True)
+#     is_active: Mapped[bool] = mapped_column(Boolean, default=True)
+#     created_at: Mapped[datetime] = mapped_column(
+#         DateTime(timezone=True), default=datetime.utcnow
+#     )
+#     updated_at: Mapped[datetime] = mapped_column(
+#         DateTime(timezone=True), default=datetime.utcnow, onupdate=datetime.utcnow
+#     )
+#
+#     tenant = relationship("Tenant", back_populates="example_items")