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/nelmio_cors.yaml

@@ -0,0 +1,10 @@
+nelmio_cors:
+    defaults:
+        origin_regex: true
+        allow_origin: ['%env(CORS_ALLOW_ORIGIN)%']
+        allow_methods: ['GET', 'OPTIONS', 'POST', 'PUT', 'PATCH', 'DELETE']
+        allow_headers: ['Content-Type', 'Authorization']
+        expose_headers: ['Link']
+        max_age: 3600
+    paths:
+        '^/': null