feat: separate current weather from forecast into distinct namespaces

- Add FORECAST namespace for multi-day outlook (12hr TTL)
- WEATHER namespace now stores only current conditions (1hr TTL)
- Split fetch_weather into fetch_current_weather + fetch_forecast
- Add POST /volatile/fetch/forecast/{city} endpoint
- Different update frequencies for efficient caching

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

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

src/models/volatile.py

@@ -18,7 +18,8 @@ class VolatileNamespace(str, Enum):
     Each namespace can have different default TTLs and refresh schedules.
     """
     # Real-time external data
-    WEATHER = "weather"          # Current conditions, forecasts
+    WEATHER = "weather"          # Current conditions (temperature, humidity, wind)
+    FORECAST = "forecast"        # Multi-day weather outlook
     SUN = "sun"                  # Sunrise, sunset, daylight duration
     NEWS = "news"                # Headlines, breaking news
     FINANCIAL = "financial"      # Stock prices, exchange rates, crypto
@@ -38,7 +39,8 @@ 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.WEATHER: 3600,       # 1 hour - current conditions
+    VolatileNamespace.FORECAST: 43200,     # 12 hours - forecast stable longer
     VolatileNamespace.SUN: 86400,          # 24 hours - sun times change daily
     VolatileNamespace.NEWS: 3600,          # 1 hour - news cycles
     VolatileNamespace.FINANCIAL: 300,      # 5 min - markets move fast