Weather/Temperature Integration (Issue #62)
Backend
- Open-Meteo API client (free, no API key) for hourly outdoor temperature
- WeatherCollector with automatic 90-day historical backfill
- API endpoints:
/api/weather,/api/weather/current,/api/weather/range - Settings UI panel with enable toggle + coordinates input
- Demo mode with 270 days synthetic temperature data
- i18n support (EN, DE, FR, ES)
Frontend Overlay
- Signal Trends: Dashed orange temperature line on secondary Y-axis (°C) on all 4 charts, with toggle button and zoom modal support
- Correlation Analysis: Toggleable temperature line with own scaling, legend entry, tooltip values, and highlight dots
29 new tests, 637 total passing.