Add QDRANT_API_KEY support to rag-service

- Add QDRANT_API_KEY to config.py (empty string = no auth)
- Pass api_key to QdrantClient constructor (None when empty)
- Add QDRANT_API_KEY to coolify compose and env example

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

rag-service/qdrant_client_wrapper.py

@@ -46,7 +46,11 @@ class QdrantClientWrapper:
     @property
     def client(self) -> QdrantClient:
         if self._client is None:
-            self._client = QdrantClient(url=settings.QDRANT_URL, timeout=30)
+            self._client = QdrantClient(
+                url=settings.QDRANT_URL,
+                api_key=settings.QDRANT_API_KEY or None,
+                timeout=30,
+            )
             logger.info("Connected to Qdrant at %s", settings.QDRANT_URL)
         return self._client