feat(web): the website and API in ping-collector; Matrix gets the ntfy transitions

Phase 3 of docs/RUST_REWRITE.md: rust/collector/src/web (axum) serves what
the FastAPI app (src/web_api.py) served, so one process collects, forecasts,
notifies and serves. With WEB_LISTEN=0.0.0.0:8000 it runs inside
`ping-collector run`; `ping-collector serve` runs it alone.

Same routes, parameters, JSON fields and field order, status codes,
{"detail": ...} errors and pydantic-style 422 lists, Cache-Control, gzip
(>500 B), CORS, Umami API tracking, the dashboard and static files, and the
stale-while-revalidate response caches (now with byte budgets: a history
response can be 10 MB). /docs is the same Swagger UI (+ /redoc); its OpenAPI
document is built from the route table, whose per-route parameter
declarations also validate the requests, so docs and behaviour cannot drift.
Python output conventions are kept: isoformat(), round(), numpy's pairwise
sums (catchment means), Python's summation order (skill metrics).

scripts/api_parity.py compares the two servers route by route on one
database (53 cases incl. errors, admin and static files; query values vary
per run so FastAPI's caches answer fresh). Locally: 53 identical; the
station CRUD writes byte-identical stations.json files; the skill/trend
logic matches on 9 station/horizon pairs with synthetic model versions.
Intended differences: /health counts the ThaiWater telemetry of the same
gauges while RID lags (as the notifier); /scraping/status adds the collector
version and last forecast run; an old stored forecast is served marked
X-Data-Stale instead of recomputed; /sensors/thaiwater is cached a minute;
.geojson is served as application/geo+json. Load (local, 16 clients): the
dashboard's routes 1375 vs 552 req/s, uncached history 714 vs 53 req/s;
25 MB resident when serving only.

Matrix (MATRIX_*): the notifier sends the room the transitions ntfy gets
(per station, outlook, feed; not ntfy's per-topic summaries), each once,
with its own matrix: keys in notification_state, seeded from ntfy's on first
use so nothing already announced repeats. Checked against a fake homeserver.
It replaces the `run.py --alert-check` cron job (repeated alerts every 15
min), which install_collector.sh now comments out (crontab backup kept).

install_collector.sh: --check-api (ping-collector serve on :8001 next to
FastAPI, api_parity.py), --cutover-api (refuses on a difference; sets
WEB_LISTEN, stops and disables water-monitor.service), --rollback-api;
--rollback-forecast and --rollback bring the Python app back as server.
ping-collector.service: MemoryMax 512M. Config::from_vars for tests; route
tests against a throwaway schema.

docs/MATRIX_QUICK_START.md

@@ -41,45 +41,43 @@ MATRIX_ROOM_ID=!your_room_id:matrix.org
 GRAFANA_URL=http://localhost:3000
 ```
 
-## Step 5: Test Configuration
+## Step 5: Restart and check
+The Matrix messages are sent by `ping-collector` (the Rust service, with
+`FORECAST_IN_COLLECTOR=true`), together with the ntfy notifications:
+
 ```bash
-# Test Matrix connection
-uv run python run.py --alert-test
-
-# Check system status (shows Matrix config)
-uv run python run.py --status
-
-# Run alert check
-uv run python run.py --alert-check
+sudo systemctl restart ping-collector
+journalctl -u ping-collector | grep -i matrix      # "Matrix notifications: room ... on ..."
+# what would be sent right now (ntfy and Matrix), changing nothing:
+sudo -u water-monitor /opt/thailand-water-monitor/bin/ping-collector notify --dry-run
 ```
 
-## Example Alert Message
-When thresholds are exceeded, you'll receive messages like:
+## What the room receives
+The same transitions as the ntfy topics (docs/NOTIFICATIONS.md), each once:
+a station crossing its warning or danger level and back (0.10 m hysteresis),
+the P.1 early-warning outlook turning on and off, and the gauge feed going
+stale or recovering. ntfy's per-topic summaries ("Ping River: warning level
+reached") are not repeated in the room. For example:
+
 ```
-🌊 **WATER LEVEL ALERT**
+⚠️ **Warning level at P.1**
+Nawarat Bridge, Chiang Mai city: 3.75 m at 18 Oct 14:00, above the warning level of 3.70 m.
 
-**Station:** P.1 (สถานีเชียงใหม่)
-**Alert Type:** Critical Water Level
-**Severity:** CRITICAL
-
-**Current Level:** 6.75m
-**Threshold:** 6.0m
-**Difference:** +0.75m
-**Discharge:** 450.2 cms
-
-**Time:** 2025-09-26 14:30:00
-
-📈 View dashboard: http://localhost:3000
+📈 Dashboard: https://water.buildfor.life/
 ```
 
-## Cron Job Setup (Optional)
-Add to crontab for automatic alerting:
-```bash
-# Check water levels every 15 minutes
-*/15 * * * * cd /path/to/monitor && uv run python run.py --alert-check >> alerts.log 2>&1
-```
+The room has its own delivery state (`matrix:` keys in `notification_state`),
+so a Matrix outage is retried on Matrix only and does not re-send ntfy.
+
+The old `run.py --alert-check` cron job (every 15 minutes, repeating an alert
+for as long as a level stayed high) is replaced by this;
+`scripts/install_collector.sh` comments it out of the crontab once
+ping-collector sends Matrix, keeping a backup next to the app.
 
 ## Troubleshooting
-- **403 Error**: Check Matrix access token is valid
-- **Room Not Found**: Verify room ID includes `!` prefix and `:homeserver.com` suffix
-- **No Alerts**: Check database has recent data with `uv run python run.py --status`
+- **HTTP 401/403** in `journalctl -u ping-collector`: the access token is invalid
+  or the account is not in the room.
+- **Room not found**: the room ID needs the `!` prefix and the `:homeserver`
+  suffix.
+- **Nothing sent**: there was no transition; `ping-collector notify --dry-run`
+  shows the readings judged and what would be sent.