Auto-populate weather data from Open-Meteo API

[bgorzelic]

Description

When an observation has GPS coordinates, automatically fetch current weather conditions from the Open-Meteo API and pre-fill relevant fields. The WeatherResponse type already exists in @firevector/schema but is not yet integrated.

Open-Meteo Integration

Open-Meteo is free, no API key required. Relevant endpoints:

• Current weather: https://api.open-meteo.com/v1/forecast?latitude=X&longitude=Y&current=temperature_2m,relative_humidity_2m,wind_speed_10m,wind_direction_10m,wind_gusts_10m

Proposed Implementation

1. Server-side API route (/api/weather): accepts lat/lng, fetches from Open-Meteo, returns structured weather data
2. Client-side trigger: When GPS coordinates are set (either manual or auto-locate), offer a "Fetch Weather" button
3. Auto-fill fields: Relative humidity, eye-level wind speed (10m wind ≈ eye-level)
4. Weather metadata: Store fetch timestamp, source, and coordinates used (the weather_meta field in schema)
5. DB schema update: Add weather_meta JSONB column or individual columns to observations table

Acceptance Criteria

• "Fetch Weather" button appears when lat/lng are populated
• Open-Meteo data pre-fills RH and wind speed fields
• User can override auto-filled values
• Weather source and timestamp are stored with observation
• Graceful fallback if Open-Meteo is unavailable
• Loading state while fetching weather
• Works for both new and edited observations