Update site builder configurations and enhance migration dependencies

- Added `OptimizationConfig` to `INSTALLED_APPS` in `settings.py`.
- Updated migration dependencies in `0001_initial.py` to include `writer` for content source fields.
- Modified the `account` ForeignKey in `PageBlueprint` and `SiteBlueprint` models to use `tenant_id` for better clarity.
- Deleted obsolete implementation plan documents for phases 0-4 to streamline project documentation.
- Improved overall project structure by removing outdated files and enhancing migration clarity.

backend/igny8_core/business/optimization/apps.py

@@ -0,0 +1,8 @@
+from django.apps import AppConfig
+
+
+class OptimizationConfig(AppConfig):
+    default_auto_field = 'django.db.models.BigAutoField'
+    name = 'igny8_core.business.optimization'
+    verbose_name = 'Optimization'
+