normalizers/nws: add NWS alerts normalizer and canonical alert mapping

- Introduce AlertsNormalizer to convert Raw NWS Alerts (SchemaRawNWSAlertsV1)
  into canonical WeatherAlert runs (SchemaWeatherAlertV1)
- Add minimal NWS alerts response/types to support GeoJSON FeatureCollection parsing
- Map NWS alert properties (event, headline, severity, timing, area, references)
  into model.WeatherAlert with best-effort timestamp handling
- Establish clear AsOf / EffectiveAt policy for alert runs to support stable
  deduplication and snapshot semantics
- Register the new alerts normalizer alongside existing NWS observation and
  forecast normalizers

cmd/weatherfeeder/config.yml

@@ -48,22 +48,30 @@ sources:
 #      url: "https://api.weather.gov/gridpoints/LSX/90,74/forecast"
 #      user_agent: "HomeOps (eric@maximumdirect.net)"
 
-  - name: NWSHourlyForecastSTL
-    kind: forecast
-    driver: nws_forecast
-    every: 1m
-    params:
-      url: "https://api.weather.gov/gridpoints/LSX/90,74/forecast/hourly"
-      user_agent: "HomeOps (eric@maximumdirect.net)"
-
-#  - name: NWSAlertsSTL
-#    kind: alert
-#    driver: nws_alerts
+#  - name: NWSHourlyForecastSTL
+#    kind: forecast
+#    driver: nws_forecast
 #    every: 1m
 #    params:
-#      url: "https://api.weather.gov/alerts?point=38.6239,-90.3571&limit=500"
+#      url: "https://api.weather.gov/gridpoints/LSX/90,74/forecast/hourly"
 #      user_agent: "HomeOps (eric@maximumdirect.net)"
 
+  - name: NWSAlertsSTL
+    kind: alert
+    driver: nws_alerts
+    every: 1m
+    params:
+      url: "https://api.weather.gov/alerts?point=38.6239,-90.3571&limit=500"
+      user_agent: "HomeOps (eric@maximumdirect.net)"
+
+  - name: NWSAlertsIowa
+    kind: alert
+    driver: nws_alerts
+    every: 1m
+    params:
+      url: "https://api.weather.gov/alerts/active/zone/IAZ048"
+      user_agent: "HomeOps (eric@maximumdirect.net)"
+
 sinks:
   - name: stdout
     driver: stdout