✨ Add day/night weather icons

[Tairesh]

Summary

Render distinct ASCII art and emoji for Clear and PartlyCloudy conditions when it is night-time at the queried location, populated from each provider's API where available and falling back to a local solar-altitude calculation otherwise.

• New Weather.is_day: Option<bool> (also surfaced in JSON output); location_name, latitude, longitude bundled into a single Weather.location: Location field.
• New src/weather/sun.rs — pure NOAA low-precision solar altitude function (no I/O, no API key).
• New src/weather/enrich.rs — post-provider wrapper that fills missing is_day (from sun) and uv_index (from OpenUV); single integration point in App::fetch_with_fallback so live mode picks it up automatically.
• Native is_day for: open_meteo (is_day query var), weather_api (is_day field), yr (_day/_night suffix on symbol_code), open_weather_map (d/n suffix on icon code), weather_bit (pod field).
• Solar-altitude fallback for: tomorrow_io and world_weather_online.
• world_weather_online fix: add includelocation=yes, parse nearest_area for coordinates, share name shortener with tomorrow_io, trim trailing space in description.
• Lift OpenUV calls out of three providers (open_meteo, open_weather_map, yr) into the shared enrich wrapper.

Test Plan

• just check passes (fmt, build, 141 tests, clippy pedantic)
• New unit tests: solar altitude (14 cases — polar/equator/antimeridian/mid-latitude/leap and non-leap years), enrich wrapper (5), shorten_location_name (5), icon module (4), formatter night/day rendering (2), per-provider parsing (6+)
• New WWO fixture at tests/data/wwo_response.json with parsing test (file had zero parsing tests before)
• Smoke-tested live: open_meteo (Tokyo/London), world_weather_online (London is_day: false, Tokyo is_day: true), tomorrow_io (Batumi shortener still works after refactor)
• Manual verification by reviewer with their own API keys for paid providers

[gemini-code-assist]

Code Review

This pull request introduces day/night awareness by adding an "is_day" field to the Weather model and updating weather providers to populate it. It also replaces the "location_name" string with a structured Location object. A new enrich module is added to calculate daytime status using solar altitude algorithms in sun.rs or extract it from various weather providers. Display logic in formatter.rs and icons.rs now uses this information to show appropriate icons and emojis for night time. A potential issue was identified in the solar altitude calculation where floating-point precision could lead to NaN results in asin(), and a fix was suggested.