Add a rain nowcast (Open-Meteo 15-minutely precipitation — worldwide, no API
key) as both an on-demand `rain`/`nowcast` command and an opt-in Weather_Service
push that announces rain starting and stopping at the bot's position.
- modules/commands/rain_command.py — command plus pure, unit-tested
fetch/analyze/dedup/label helpers (also reused by the service)
- modules/service_plugins/weather_service.py — background poller mirroring the
existing weather-alert poll pattern; ships disabled (opt-in)
- Location labels resolve to "City, ST" (US) / "City, Country" (non-US)
- 34 unit tests; rain_command added to the strict-mypy module list