release: v1.6.1 - Weather forecasts, sun times, air quality

- Weather fetch now returns 7-day forecasts with UV index
- New /volatile/fetch/sun/{city} endpoint for sunrise/sunset
- New /volatile/fetch/air_quality/{city} endpoint for AQI and pollutants
- OpenMeteoProvider now implements AirQualityProvider interface

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/models/volatile.py

@@ -19,6 +19,7 @@ class VolatileNamespace(str, Enum):
     """
     # Real-time external data
     WEATHER = "weather"          # Current conditions, forecasts
+    SUN = "sun"                  # Sunrise, sunset, daylight duration
     NEWS = "news"                # Headlines, breaking news
     FINANCIAL = "financial"      # Stock prices, exchange rates, crypto
     TRANSIT = "transit"          # Train/bus schedules, delays, disruptions
@@ -38,6 +39,7 @@ class VolatileNamespace(str, Enum):
 # Default TTLs per namespace (in seconds)
 NAMESPACE_DEFAULT_TTL: Dict[str, int] = {
     VolatileNamespace.WEATHER: 1800,       # 30 min - weather changes slowly
+    VolatileNamespace.SUN: 86400,          # 24 hours - sun times change daily
     VolatileNamespace.NEWS: 3600,          # 1 hour - news cycles
     VolatileNamespace.FINANCIAL: 300,      # 5 min - markets move fast
     VolatileNamespace.TRANSIT: 300,        # 5 min - schedules update frequently