fix(health): report unhealthy memory vector store as degraded

Keep an unhealthy MemoryVectorStore instance available for health reporting instead of discarding it as disabled. This lets health checks report a degraded/down vector-store state while preserving focused regression coverage for initializer behavior.

src/app_initializer.py

@@ -68,8 +68,10 @@ def initialize_managers(base_dir: str, rag_manager=None) -> Dict[str, Any]:
                     logger.info(f"Rebuilt memory vector index from {len(existing)} existing entries")
             logger.info("MemoryVectorStore initialized")
         else:
+            # Keep the unhealthy object (do NOT reset to None): consumers gate on
+            # `.healthy`, and service_health.chromadb_health() needs a present
+            # object to report DEGRADED/DOWN instead of DISABLED ("not configured").
             logger.warning("MemoryVectorStore DEGRADED: ChromaDB vector memory unavailable")
-            memory_vector = None
     except Exception as e:
         logger.warning(f"MemoryVectorStore DEGRADED: {e}")
         memory_vector = None