Add get_nearby_weather_stations/4 query function with spatial filtering
Implements PostGIS-based query to find weather stations within a radius:
- Uses ST_DWithin for efficient spatial filtering within radius (miles to meters)
- Orders results by ST_Distance (closest first)
- Filters by has_weather, has_position, and time window (default 6h)
- Deduplicates by base_callsign using DISTINCT ON (avoids duplicate SSIDs)
- Returns all weather fields: temp, humidity, pressure, wind, rain
- Configurable limit (default 50) and hours options
Comprehensive test coverage (10 tests):
- Spatial filtering within/outside radius
- Time window filtering
- Base callsign deduplication (most recent SSID)
- Distance ordering verification
- Required field validation
- Edge cases (empty results, no weather data)
Graham McIntire
47fc071263