feat: RID large-dam daily collector — Mae Ngat storage/inflow/outflow

POST app.rid.go.th/reservoir/api/dams (open, archive >=2009) collected
hourly into rid_dams + rid_reservoir_daily; backfill script fetches only
missing days so reruns repair holes and are safe alongside the live
collector. /api/stats counts the new table via an engine fallback that
works when HII collection is disabled. Mae Ngat (DAM_ID 200103) hit 113%
usable capacity with ~19 MCM/day inflow in the Oct 2024 flood — candidate
features for the next retrain.

scripts/backfill_rain_db.py

@@ -26,7 +26,9 @@ def main(argv=None) -> int:
         level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s"
     )
     if args.db_url:
-        connection_string, db_type = args.db_url, args.db_url.split(":", 1)[0]
+        # postgresql+psycopg2://... -> postgresql (driver suffix is not a dialect)
+        connection_string = args.db_url
+        db_type = args.db_url.split(":", 1)[0].split("+", 1)[0]
     else:
         cfg = Config.get_database_config()
         if cfg["type"] not in ("sqlite", "postgresql", "mysql"):