feat: production deployment - full update with providers, admin, glossaries, pricing, tests

Major changes across backend, frontend, infrastructure:
- Provider system with model selection (Google, DeepL, OpenAI, Ollama, Google Cloud)
- Admin panel: user management, pricing, settings
- Glossary system with CSV import/export
- Subscription and tier quota management
- Security hardening (rate limiting, API key auth, path traversal fixes)
- Docker compose for dev, prod, and IONOS deployment
- Alembic migrations for new tables
- Frontend: dashboard, pricing page, landing page, i18n (en/fr)
- Test suite and verification scripts

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docker/nginx/nginx.conf

@@ -58,6 +58,14 @@ http {
     limit_req_zone $binary_remote_addr zone=upload_limit:10m rate=2r/s;
     limit_conn_zone $binary_remote_addr zone=conn_limit:10m;
 
+    # CORS: allow same-origin only (and localhost for dev). Override in conf.d if you need multiple origins.
+    map $http_origin $cors_origin {
+        default "";
+        "~^https?://$host(:[0-9]+)?$" $http_origin;
+        "~^https?://127\.0\.0\.1(:[0-9]+)?$" $http_origin;
+        "~^https?://localhost(:[0-9]+)?$" $http_origin;
+    }
+
     # Upstream definitions
     upstream backend {
         server backend:8000;