T03: plugin system framework + lifecycle + migrations + event bus + DI

- Plugin registry with discover/install/activate/deactivate/uninstall lifecycle
- PluginManifest Pydantic v2 schema (name, version, dependencies, routes, events, migrations)
- BasePlugin abstract class with lifecycle hooks (on_install/activate/deactivate/uninstall)
- Migration runner with tenant_id validator (rejects tables without tenant_id)
- Event bus integration: register/unregister listeners on activate/deactivate
- Service container DI: plugins receive db, cache, event_bus, storage, notifications
- Idempotent operations (activate active=200, deactivate inactive=200)
- UI registry for frontend component registration
- 47 new tests (14 ACs + 33 unit tests), 103 total tests pass
- Migration 0003: plugins + plugin_migrations tables
- Coverage: 85.92% for plugin modules

app/main.py

@@ -9,14 +9,26 @@ from fastapi.middleware.cors import CORSMiddleware
 
 from app.config import get_settings
 from app.core.middleware import CSRFMiddleware
-from app.core.db import close_engine
-from app.routes import auth, users, roles, tenants, health, notifications, companies, contacts, import_export
+from app.core.db import close_engine, get_engine
+from app.core.service_container import get_container
+from app.plugins.registry import get_registry
+from app.routes import auth, users, roles, tenants, health, notifications, companies, contacts, import_export, plugins
 
 
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     """Application lifespan: startup and shutdown."""
+    # Initialize service container
+    container = get_container()
+    await container.initialize()
+
+    # Initialize plugin registry and discover built-in plugins
+    registry = get_registry()
+    registry.initialize(get_engine(), app)
+    registry.discover_builtins()
+
     yield
+
     await close_engine()
 
 
@@ -44,6 +56,7 @@ def create_app() -> FastAPI:
     app.include_router(companies.router)
     app.include_router(contacts.router)
     app.include_router(import_export.router)
+    app.include_router(plugins.router)
 
     return app