Add site builder service to Docker Compose and remove obsolete scripts

- Introduced a new service `igny8_site_builder` in `docker-compose.app.yml` for site building functionality, including environment variables and volume mappings.
- Deleted several outdated scripts: `create_test_users.py`, `test_image_write_access.py`, `update_free_plan.py`, and the database file `db.sqlite3` to clean up the backend.
- Updated Django settings and URL configurations to integrate the new site builder module.

backend/igny8_core/settings.py

@@ -52,6 +52,8 @@ INSTALLED_APPS = [
     'igny8_core.modules.system.apps.SystemConfig',
     'igny8_core.modules.billing.apps.BillingConfig',
     'igny8_core.modules.automation.apps.AutomationConfig',
+    'igny8_core.business.site_building.apps.SiteBuildingConfig',
+    'igny8_core.modules.site_builder.apps.SiteBuilderConfig',
 ]
 
 # System module needs explicit registration for admin