Add configuration files and comprehensive project documentation

- Add .env.backup with full application configuration template
- Create RequestIDMiddleware for trace ID injection in logs
- Implement ARQ fallback pool for Redis unavailability
- Add Dead Letter Queue module for failed job handling
- Include project ROADMAP with audit and 27 applied corrections
- Add Grafana monitoring dashboard with 10 panels

app/workers/arq_fallback.py

@@ -0,0 +1,24 @@
+"""
+Module partagé pour le fallback ARQ — évite les imports circulaires.
+
+Fournit _FallbackArqPool et is_fallback_pool().
+"""
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+class _FallbackArqPool:
+    """Fallback quand Redis/ARQ n'est pas disponible."""
+
+    async def enqueue_job(self, *args, **kwargs):
+        logger.warning("arq.fallback_enqueue", extra={"args": str(args)})
+        return None
+
+    async def close(self):
+        pass
+
+
+def is_fallback_pool(pool) -> bool:
+    """Vérifie si un pool ARQ est le fallback (Redis indisponible)."""
+    return isinstance(pool, _FallbackArqPool)