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/schemas/space.py

@@ -20,7 +20,7 @@ class SpaceBase(BaseModel):
 class SpaceCreate(SpaceBase):
     """Space creation schema."""
 
-    pass
+    property_id: int | None = None
 
 
 class SpaceUpdate(SpaceBase):
@@ -40,6 +40,8 @@ class SpaceResponse(SpaceBase):
 
     id: int
     is_active: bool
+    property_id: int | None = None
+    property_name: str | None = None
     working_hours_start: int | None = None
     working_hours_end: int | None = None
     min_duration_minutes: int | None = None