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>

services/providers/fallback.py

@@ -14,16 +14,10 @@ Features:
 from typing import List, Optional, Dict, Any
 import time
 
-try:
-    import structlog
+from core.logging import get_logger
 
-    logger = structlog.get_logger(__name__)
-    _HAS_STRUCTLOG = True
-except ImportError:
-    import logging
-
-    logger = logging.getLogger(__name__)
-    _HAS_STRUCTLOG = False
+logger = get_logger(__name__)
+_HAS_STRUCTLOG = True
 
 
 def _log_info(event: str, **kwargs):
@@ -332,6 +326,41 @@ class LegacyFallbackAdapter:
         source_language: str = "auto",
         batch_size: int = 50,
     ) -> List[str]:
+        if not texts:
+            return []
+
+        from .config import ProvidersConfig
+
+        provider_names = ProvidersConfig.get_fallback_chain(self._mode)
+        requests = [
+            TranslationRequest(
+                text=t,
+                target_language=target_language,
+                source_language=source_language,
+            )
+            for t in texts
+        ]
+
+        # Try each provider once with a full batch (avoids N× fallback chain walks).
+        for provider_name in provider_names:
+            p = registry.get(provider_name)
+            if p is None:
+                continue
+            if not p.is_available():
+                continue
+            try:
+                responses = p.translate_batch(requests)
+            except Exception:
+                continue
+            if len(responses) != len(requests):
+                continue
+            if all(r.error is None for r in responses):
+                self._last_provider_used = provider_name
+                return [
+                    r.translated_text if r.translated_text is not None else texts[i]
+                    for i, r in enumerate(responses)
+                ]
+
         results: List[str] = []
         for t in texts:
             req = TranslationRequest(