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.

requirements.txt

@@ -1,34 +1,9 @@
-# Core dependencies
+# Python side: flood-model training, evaluation, backfills (pyproject.toml is
+# the source; uv.lock pins the rest). The service is ping-collector (rust/).
 requests==2.34.2
-schedule==1.2.0
 pandas==2.0.3
 numpy>=1.24,<2  # pandas 2.0.3 wheels are ABI-incompatible with numpy 2.x
-
-# Flood forecasting (ML)
 scikit-learn==1.9.0
-
-# Web API framework
-fastapi==0.141.1
-uvicorn[standard]==0.52.4
-pydantic==2.13.5
-
-# Database adapters
 sqlalchemy==2.0.23
-influxdb==5.3.1
-pymysql==1.2.0
 psycopg2-binary==2.9.9
-
-# Monitoring and metrics
-psutil==5.9.6
-
-# Development dependencies (optional)
-pytest==9.1.1
-pytest-cov==4.1.0
-black==26.5.1
-flake8==6.1.0
-mypy==1.7.1
-pre-commit==3.5.0
-
-# Documentation
-sphinx==7.2.6
-sphinx-rtd-theme==1.3.0
+python-dotenv==1.1.1