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_hii_fill.py

@@ -28,12 +28,13 @@ def _base_frame(code="P.20", n=200, level=2.0):
 
 
 @pytest.fixture
-def hii_db(tmp_path):
-    """SQLite DB with hii_* tables; returns (db_url, store)."""
-    db_url = f"sqlite:///{tmp_path}/hii_fill.db"
-    store = HiiStore(db_url, "sqlite")
+def hii_db(pg_url):
+    """A schema with the hii_* tables; returns (db_url, store)."""
+    store = HiiStore(pg_url)
     assert store.connect()
-    return db_url, store
+    yield pg_url, store
+    store.engine.dispose()
+
 
 def _seed_mirror(store, station_id, rid_code, hours, wl_msl, discharge=250.0):
     from sqlalchemy import text
@@ -113,9 +114,9 @@ class TestFillFromHii:
         filled = fill_from_hii(base, db_url, min_overlap_hours=1)
         assert len(filled) == len(base)  # P.76 not in HII_FILL_STATIONS
 
-    def test_missing_tables_degrade_gracefully(self, tmp_path):
+    def test_missing_tables_degrade_gracefully(self, pg_url):
         base = _base_frame("P.20")
-        filled = fill_from_hii(base, f"sqlite:///{tmp_path}/empty.db")
+        filled = fill_from_hii(base, pg_url)  # empty schema: no hii_* tables
         assert filled.equals(base)
 
     def test_no_station_overlap_returns_input(self, hii_db):