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.

src/config.py

@@ -86,6 +86,11 @@ class Config:
         "yes",
     )
     HII_BASIN_CODE = int(os.getenv("HII_BASIN_CODE", "6"))  # 6 = Ping Basin
+
+    # RID large-dam daily status (app.rid.go.th/reservoir) — Mae Ngat et al.
+    ENABLE_RESERVOIR_COLLECTION = os.getenv(
+        "ENABLE_RESERVOIR_COLLECTION", "true"
+    ).lower() in ("1", "true", "yes")
     # TTL for the /api/hii/*/latest response cache; source data changes hourly
     HII_CACHE_TTL_SECONDS = int(os.getenv("HII_CACHE_TTL_SECONDS", "120"))
     # TTL for the /measurements/latest response cache (hottest endpoint)