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.

.gitea/workflows/docs.yml

@@ -1,36 +1,23 @@
 name: Docs
 
-# Checks that the documentation the project actually ships stays consistent:
-#   - every relative link / image path in docs/*.md and README.md resolves
-#     inside the repo (external URLs are NOT fetched: localhost examples,
-#     rate-limited hosts and the Tailscale-era links made that gate permanently
-#     red, and a 200 on a curl --head proves nothing about a doc anyway)
-#   - the FastAPI app imports and its OpenAPI schema is exportable (that is
-#     the reference at https://water.buildfor.life/docs)
-# The previous Sphinx/apidoc jobs produced artifacts nobody read and were
-# removed. Reference docs live in docs/*.md; the public overview is at
-# https://buildfor.life/docs/tooling/ping-river-monitor/.
+# Every relative link / image path in the shipped Markdown (README, CLAUDE,
+# CONTRIBUTING, rust/README, docs/) resolves inside the repo. External URLs
+# are NOT fetched: localhost examples and rate-limited hosts made that gate
+# permanently red, and a 200 proves nothing about a doc anyway. The API
+# reference (/docs, /openapi.json) is generated by ping-collector from its
+# route table and tested in rust/collector/src/web/tests.rs.
 
 on:
   push:
     branches: [master, develop]
     paths:
-      - "docs/**"
-      - "README.md"
-      - "CONTRIBUTING.md"
-      - "src/web_api.py"
-      - "src/schemas.py"
+      - "**.md"
       - ".gitea/workflows/docs.yml"
   pull_request:
     paths:
-      - "docs/**"
-      - "README.md"
-      - "CONTRIBUTING.md"
+      - "**.md"
   workflow_dispatch:
 
-env:
-  PYTHON_VERSION: "3.11"
-
 jobs:
   docs:
     name: Validate documentation
@@ -43,7 +30,8 @@ jobs:
           python3 - <<'PY'
           import re, sys, pathlib
           root = pathlib.Path(".")
-          files = [root / "README.md", root / "CONTRIBUTING.md", *root.glob("docs/**/*.md")]
+          files = [root / "README.md", root / "CLAUDE.md", root / "CONTRIBUTING.md",
+                   root / "rust" / "README.md", *root.glob("docs/**/*.md")]
           link = re.compile(r"!?\[[^\]]*\]\(([^)\s]+)(?:\s+\"[^\"]*\")?\)")
           bad = []
           for md in files:
@@ -65,35 +53,3 @@ jobs:
               sys.exit(1)
           print(f"checked {len(files)} files, all relative links resolve")
           PY
-
-      - uses: actions/setup-python@v5
-        with:
-          python-version: ${{ env.PYTHON_VERSION }}
-          cache: pip
-          cache-dependency-path: requirements.txt
-
-      - name: Install dependencies
-        run: |
-          python -m pip install --upgrade pip --root-user-action=ignore
-          pip install --root-user-action=ignore -r requirements.txt
-
-      - name: OpenAPI schema exports
-        env:
-          DB_TYPE: sqlite
-        run: |
-          python - <<'PY'
-          import json
-          from src.web_api import app
-          spec = app.openapi()
-          paths = sorted(spec["paths"])
-          required = {"/forecast", "/measurements/latest", "/measurements/history/{station_code}", "/stations", "/api/stats", "/health"}
-          missing = required - set(paths)
-          assert not missing, f"documented endpoints missing from the app: {missing}"
-          json.dump(spec, open("openapi.json", "w"), indent=1)
-          print(f"{len(paths)} paths; schema written to openapi.json")
-          PY
-
-      - uses: actions/upload-artifact@v3
-        with:
-          name: openapi-${{ github.run_number }}
-          path: openapi.json