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.

tests/test_dam_features.py

@@ -51,7 +51,7 @@ class TestHourlyFrame:
 
 
 class TestLoadDaily:
-    def test_empty_db_result_does_not_wipe_cache(self, tmp_path):
+    def test_empty_db_result_does_not_wipe_cache(self, tmp_path, pg_url):
         from sqlalchemy import create_engine, text
 
         from src.ml.dam import CACHE_FILE, load_daily
@@ -60,15 +60,16 @@ class TestLoadDaily:
         cache_path = tmp_path / CACHE_FILE
         _daily(3).rename_axis("date").to_csv(cache_path, compression="gzip")
         # Reachable DB whose table exists but is empty
-        db = f"sqlite:///{tmp_path}/empty_dam.db"
-        with create_engine(db).begin() as conn:
+        engine = create_engine(pg_url)
+        with engine.begin() as conn:
             conn.execute(
                 text(
                     "CREATE TABLE rid_reservoir_daily (dam_id TEXT, date DATE, "
                     "storage_pct REAL, inflow_mcm REAL, outflow_mcm REAL)"
                 )
             )
-        result = load_daily(db_url=db, cache_dir=tmp_path)
+        engine.dispose()
+        result = load_daily(db_url=pg_url, cache_dir=tmp_path)
         assert result.empty  # honest empty result...
         cached = pd.read_csv(cache_path, index_col=0)
         assert len(cached) == 3  # ...but the good cache survives
@@ -122,7 +123,8 @@ class TestFeatureGating:
         dam = hourly_frame(_daily(days=20, start="2024-09-10"))
         X = features.build_features(grid, "P.1", dam=dam)
         ts = pd.Timestamp("2024-09-24 12:00")
-        expected = X.loc[ts, "dam_storage_pct"] - X.loc[
-            ts - pd.Timedelta(hours=72), "dam_storage_pct"
-        ]
+        expected = (
+            X.loc[ts, "dam_storage_pct"]
+            - X.loc[ts - pd.Timedelta(hours=72), "dam_storage_pct"]
+        )
         assert abs(X.loc[ts, "dam_storage_pct_d3"] - expected) < 1e-9