fix(analytics): add _conn module-level override for test patching

Tests monkeypatch analytics._conn to inject a temp DuckDB connection.
The attribute didn't exist; fetch_analytics now uses it when set,
bypassing the _db_path / threading.local path.

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

web/src/beanflows/analytics.py

@@ -65,6 +65,7 @@ ALLOWED_METRICS = frozenset({
 
 _local = threading.local()
 _db_path: str = ""
+_conn: duckdb.DuckDBPyConnection | None = None  # test override: set to bypass _db_path / _local
 
 
 def open_analytics_db() -> None:
@@ -110,12 +111,15 @@ async def fetch_analytics(sql: str, params: list | None = None) -> list[dict]:
     """Run a read-only DuckDB query off the event loop. Returns list of dicts.
     Returns empty list if analytics DB is not configured (SERVING_DUCKDB_PATH unset
     or file missing at startup) — dashboard routes degrade gracefully.
+
+    If the module-level _conn is set (test override), it is used directly in place
+    of the per-thread _get_conn() path.
     """
-    if not _db_path:
+    if _conn is None and not _db_path:
         return []
 
     def _query():
-        conn = _get_conn()
+        conn = _conn if _conn is not None else _get_conn()
         cursor = conn.cursor()
         result = cursor.execute(sql, params or [])
         columns = [desc[0] for desc in result.description]