feat: add multi-tenant system with properties, organizations, and public booking

Implement complete multi-property architecture:
- Properties (groups of spaces) with public/private visibility
- Property managers (many-to-many) with role-based permissions
- Organizations with member management
- Anonymous/guest booking support via public API (/api/public/*)
- Property-scoped spaces, bookings, and settings
- Frontend: property selector, organization management, public booking views
- Migration script and updated seed data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -11,6 +11,12 @@ from app.api.bookings import bookings_router
 from app.api.bookings import router as spaces_bookings_router
 from app.api.google_calendar import router as google_calendar_router
 from app.api.notifications import router as notifications_router
+from app.api.organizations import admin_router as organizations_admin_router
+from app.api.organizations import router as organizations_router
+from app.api.properties import admin_router as properties_admin_router
+from app.api.properties import manager_router as properties_manager_router
+from app.api.properties import router as properties_router
+from app.api.public import router as public_router
 from app.api.reports import router as reports_router
 from app.api.settings import router as settings_router
 from app.api.spaces import admin_router as spaces_admin_router
@@ -50,6 +56,12 @@ app.include_router(audit_log_router, prefix="/api", tags=["audit-log"])
 app.include_router(attachments_router, prefix="/api", tags=["attachments"])
 app.include_router(reports_router, prefix="/api", tags=["reports"])
 app.include_router(google_calendar_router, prefix="/api", tags=["google-calendar"])
+app.include_router(properties_router, prefix="/api")
+app.include_router(properties_manager_router, prefix="/api")
+app.include_router(properties_admin_router, prefix="/api")
+app.include_router(organizations_router, prefix="/api")
+app.include_router(organizations_admin_router, prefix="/api")
+app.include_router(public_router, prefix="/api")
 
 
 @app.get("/")