fix(postgres): resolve 3 CI failures in PR QA Gate

1. keyword_ops.py: Use CAST(:metadata AS jsonb) instead of
   :metadata::jsonb — the :: cast syntax conflicts with SQLAlchemy's
   :name bind parameter parsing, producing invalid SQL in PostgreSQL.

2. connection.py: Clamp pool.overflow() with max(0, ...) in
   get_pool_status() — QueuePool.overflow() can return negative values
   when connections are below pool_size.

3. test_storage_config.py: Add monkeypatch.delenv("DATABASE_URL") to
   prevent CI's DATABASE_URL environment variable from making the
   postgres-no-config warning test pass incorrectly.

Fixes PR QA Gate run #22010406320.

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

Author: RichardHightower

agent-brain-server/agent_brain_server/storage/postgres/connection.py

@@ -193,6 +193,6 @@ async def get_pool_status(self) -> dict[str, Any]:
             "pool_size": pool.size(),
             "checked_in": pool.checkedin(),
             "checked_out": pool.checkedout(),
-            "overflow": pool.overflow(),
-            "total": pool.size() + pool.overflow(),
+            "overflow": max(0, pool.overflow()),
+            "total": pool.size() + max(0, pool.overflow()),
         }

agent-brain-server/agent_brain_server/storage/postgres/keyword_ops.py

@@ -82,7 +82,7 @@ async def upsert_with_tsvector(
                 INSERT INTO documents
                     (chunk_id, document_text, metadata, tsv)
                 VALUES (
-                    :chunk_id, :document_text, :metadata::jsonb,
+                    :chunk_id, :document_text, CAST(:metadata AS jsonb),
                     setweight(to_tsvector(
                         :language, COALESCE(:title, '')
                     ), 'A') ||

agent-brain-server/tests/unit/config/test_storage_config.py

@@ -135,8 +135,13 @@ def test_provider_settings_yaml_roundtrip_postgres() -> None:
     assert settings.storage.postgres["port"] == 5432
 
 
-def test_validate_provider_config_postgres_no_config_warning() -> None:
+def test_validate_provider_config_postgres_no_config_warning(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
     """Test validate_provider_config warns when postgres backend has no config."""
+    # Ensure DATABASE_URL is not set (CI sets it for postgres tests)
+    monkeypatch.delenv("DATABASE_URL", raising=False)
+
     settings = ProviderSettings(
         storage=StorageConfig(backend="postgres", postgres={}),
     )