chore: remove the Python service; Python is the training stack only

Phase 4 of docs/RUST_REWRITE.md. Since 2026-10-18 ping-collector (rust/)
collects, forecasts, notifies (ntfy + Matrix) and serves the website/API;
nothing in production ran the Python service code any more.

Removed (~17k lines): the FastAPI app (web_api, schemas, health_check,
metrics, postgres_history, forecast_history, thaiwater), the Python RID
collector and CLI (water_scraper_v3, main, run.py), the notifier and Matrix
alerting (notify, alerting), the multi-backend adapters (SQLite, MySQL,
InfluxDB, VictoriaMetrics) with demo databases, models/validators/exceptions/
logging/rate limiter, ml/skill.py (served by Rust now), the migration tooling
(api_parity, collector_parity, e2e_notify, install_collector.sh,
gen_notify_cases.py, spikes/rust-forecast), Docker/compose/Grafana files,
sql/, the release workflow and the docs for all of that. Their tests went
with them.

Kept in Python: src/ml (training, evaluation harness, export; predict.py as
the reference the Rust forecaster is tested against), the HII and RID-dam
clients/stores for the archive backfills (their live collectors removed),
the backfill scripts, retrain.sh + timer, forecast_parity.py.

- PostgreSQL only: src/config.py is database_url() from POSTGRES_* / .env;
  the stores lost their sqlite/mysql branches (and the 2026-08 column
  migration). The database tests run against a throwaway schema from
  TEST_DATABASE_URL (tests/conftest.py pg_url, skipped without it), as the
  Rust tests do; CI gets a PostgreSQL service. 100 tests (66 without a DB).
- The notifier settings moved from src/notify.py into src/ml/export.py;
  flood_config.json regenerates byte-identical.
- tests/test_dashboard.py checks every path the dashboard fetches against
  ping-collector's router.
- Dependencies: fastapi, uvicorn, pydantic, influxdb, pymysql, psutil,
  schedule, sphinx, pyinstaller, mypy, pytest-asyncio dropped; python-dotenv
  1.1.1 explicit (it came in through uvicorn[standard]).
- Formatting contract extended to scripts/ and tests/ (reformatted once).
- scripts/install.sh is the one installer (fresh host or update, in place in
  a checkout without touching its ownership): binary, units, uv sync, .env
  defaults, removes the retired water-monitor.service and any old
  --alert-check cron job, dry run + forecast check, restart, readiness wait.
- Docs, CLAUDE.md, CONTRIBUTING.md, .env.example, Makefile, unit comments
  and Rust doc comments updated to the Rust service.

scripts/backfill_rid_reservoir.py

@@ -3,7 +3,7 @@
 
 Two paths, both idempotent and both skipping what is already stored, so a
 rerun repairs holes left by transient failures and is safe alongside the
-hourly live collector:
+live collector (ping-collector, today + yesterday):
 
   --dam-id (default: Mae Ngat)  one dam, whole range, via api/dam — a handful
                                 of requests for the entire 2009-today archive
@@ -26,13 +26,8 @@ import sys
 
 sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
 
-from src.config import Config
-from src.rid_reservoir import (
-    MAE_NGAT_DAM_ID,
-    RidReservoirStore,
-    backfill,
-    backfill_dam,
-)
+from src.config import database_url
+from src.rid_reservoir import MAE_NGAT_DAM_ID, RidReservoirStore, backfill, backfill_dam
 
 DEFAULT_START = datetime.date(2018, 8, 1)  # start of the water_measurements grid
 
@@ -71,18 +66,14 @@ def main(argv=None) -> int:
     logging.basicConfig(
         level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s"
     )
-    if args.db_url:
-        # 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"):
-            print(f"requires a SQL database, got {cfg['type']}", file=sys.stderr)
-            return 1
-        connection_string, db_type = cfg["connection_string"], cfg["type"]
+    connection_string = args.db_url or database_url()
+    if not connection_string:
+        print(
+            "no database: set POSTGRES_CONNECTION_STRING or POSTGRES_*", file=sys.stderr
+        )
+        return 1
 
-    store = RidReservoirStore(connection_string, db_type)
+    store = RidReservoirStore(connection_string)
     if not store.connect():
         print(
             "database connection failed — check the connection string",