feat(rust): ping-collector, phase 1 of the Rust rewrite

rust/collector replaces the collection half of the Python web app: RID hourly
gauges (with the late-report semantics: store everything, retry every 10 min
while RID is behind, re-fetch yesterday's holes, startup gap fill), HII rain +
water level, RID dams (today + yesterday) and Open-Meteo rain. Same tables and
upsert semantics, one UNNEST statement per table, Bangkok wall-clock time
regardless of the server time zone.

Python side: COLLECTION_ENABLED=false makes the API leader stop collecting and
instead re-forecast + notify when the newest RID reading in the database
advances (polled every FORECAST_POLL_SECONDS) and once per clock hour;
/scraping/status then serves the collector's status file; /scrape/trigger
answers 409.

Verified: 20 Rust tests (parsers, gap/schedule logic, database tests against
PostgreSQL); live parity run of both collectors into two empty databases:
all 9 tables row-for-row identical (scripts/collector_parity.py); the Python
API served health, measurements, stats, status and model forecasts from a
database filled only by ping-collector. 177 Python tests pass.

reqwest uses native-tls: app.rid.go.th offers only TLS 1.2 CBC suites, which
rustls refuses.

Deploy/cutover/rollback: scripts/install_collector.sh, scripts/ping-collector.service;
CI: .gitea/workflows/rust.yml (fmt, clippy, tests with a PostgreSQL service,
release artifact).

rust/collector/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "ping-collector"
+version = "0.1.0"
+description = "Ping River Monitor data collector: RID gauges, HII/ThaiWater, RID dams, Open-Meteo rain -> PostgreSQL"
+edition.workspace = true
+license.workspace = true
+publish.workspace = true
+repository.workspace = true
+
+[dependencies]
+anyhow.workspace = true
+chrono.workspace = true
+clap.workspace = true
+dotenvy.workspace = true
+reqwest.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+sqlx.workspace = true
+tokio.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true