feat(api) : add /api/health endpoint for monitoring

- Returns status, version, timestamp, PHP version, DB latency and memory usage
- Accessible without authentication (PUBLIC_ACCESS)
- Returns 200 when healthy, 503 when degraded (DB down)

config/packages/security.yaml

@@ -55,6 +55,7 @@ security:
         - { path: ^/api/admin, roles: ROLE_ADMIN }
         - { path: ^/api/docs, roles: PUBLIC_ACCESS }
         - { path: ^/api/test, roles: PUBLIC_ACCESS }
+        - { path: ^/api/health$, roles: PUBLIC_ACCESS }
         - { path: ^/docs, roles: PUBLIC_ACCESS }
         - { path: ^/contexts, roles: PUBLIC_ACCESS }
         - { path: ^/\.well-known, roles: PUBLIC_ACCESS }