v0.48.0: m Load the ride map in one batched fetch and speed up radar playback

Ride: today
- Fetch the grid in about three multi-location Open-Meteo requests of
  rain and wind only, with Unix times and hours relative to now.
- Centre the grid on a fixed lattice so nearby positions share cells.
- Keep grid responses for 30 minutes; cap grids at 23x23 to fit the
  600-calls-a-minute free limit.
- Web views stop waiting after five seconds and show a retry note.

Radar
- Load local forecast frames in parallel, every ten minutes for an hour.
- Fetch basemap tiles and label layers concurrently.
- Preload the local observation from the page head.

Times
- Show forecast and nowcast times in the location's zone on every
  surface, never the server's.
- Stream page heads before resolving the location's zone.

Cache
- Drop expired entries on every write so large grids leave memory.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>