Phase 0 : entités, migrations, API Platform, PostGIS

- API Platform + Doctrine ORM + jsor/doctrine-postgis installés
- 6 entités Symfony (SargassumObservation, SargassumForecast,
  DataIngestionJob, CoastalPoint, ImpactScore, UserFeedback)
- Migration initiale manuelle avec CREATE EXTENSION postgis,
  toutes les tables, index GIST et BTREE
- doctrine.yaml configuré pour PostgreSQL 16 + types PostGIS
- Roadmap Phase 0 complète

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

backend/config/packages/validator.yaml

@@ -0,0 +1,11 @@
+framework:
+    validation:
+        # Enables validator auto-mapping support.
+        # For instance, basic validation constraints will be inferred from Doctrine's metadata.
+        #auto_mapping:
+        #    App\Entity\: []
+
+when@test:
+    framework:
+        validation:
+            not_compromised_password: false