Add configurable weather condition icons

[shenfy]

Summary

• add opt-in {weather_icon} and {weather_icon_day} whole-slot widget tokens
• map Open-Meteo weather codes to a stable semantic icon enum and send current/daily values to the watch
• render bundled official Pebble 25 x 25 PDC weather artwork, with native Pebble fog and lightning additions for conditions absent from the official collection
• expose text and icon condition choices in the configuration page while preserving existing {cond} and {cond_day} behavior and defaults
• add deterministic weather-code mapping coverage and document the new tokens and asset provenance

No additional weather request or phone application is introduced; this continues to use Halcyon's existing PebbleKit JS/Open-Meteo flow. Inline icon-and-text runs are intentionally out of scope for this first implementation.

Verification

• npm run test:weather-icons
• npm run check:i18n
• npm run lint in config-page (0 errors; existing warnings only)
• npm run build in config-page
• clean pebble build for Aplite, Basalt, Chalk, Diorite, Emery, Flint, and Gabbro
• visual emulator checks on Aplite, Basalt, and Chalk

Compatibility

• retains Halcyon's existing name, UUID, author metadata, license, defaults, and localized text condition tokens
• bundles all icon resources in the PBW and supports monochrome and color platforms
• caches only the current and daily PDC images and releases them during teardown