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.

rust/collector/src/config.rs

@@ -1,5 +1,7 @@
-//! Configuration from the same environment / `.env` file as the Python app,
-//! so both services can share `/opt/thailand-water-monitor/.env`.
+//! Configuration from the environment / `.env` file
+//! (`/opt/thailand-water-monitor/.env`), which the Python training tools
+//! (src/config.py) read too. Names and defaults are the ones the Python app
+//! used.
 
 use anyhow::{Context, Result, bail};
 use std::env;
@@ -33,10 +35,10 @@ pub struct Config {
     /// Days of RID holes re-fetched at startup (0 = off).
     pub gap_fill_days_on_start: u32,
     pub station_config_path: PathBuf,
-    /// Status JSON read by the Python API's /scraping/status.
+    /// Status JSON for /scraping/status when the website runs in a separate
+    /// process (`ping-collector serve`).
     pub status_file: Option<PathBuf>,
-    /// FORECAST_IN_COLLECTOR: forecast and notify here; the Python API then
-    /// serves the stored forecast and does neither.
+    /// FORECAST_IN_COLLECTOR: forecast and notify (off: collect only).
     pub forecast_enabled: bool,
     /// Exported bundles (`flood_<station>.json.gz`, src/ml/export.py).
     pub models_dir: PathBuf,
@@ -62,7 +64,7 @@ pub struct MatrixConfig {
     pub room_id: String,
 }
 
-/// The website and read API (src/web_api.py's settings, same names).
+/// The website and read API (setting names as the retired Python app had them).
 #[derive(Clone, Debug)]
 pub struct WebConfig {
     /// WEB_LISTEN: `run` also serves the website on this address