feat(models): add fire event subject routing

Update subject_for_event to handle fire.* category events:
- Fire events: central.<category> (e.g., central.fire.hotspot.viirs_snpp.high)
- Weather events: existing geo-based subject logic

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

src/central/models.py

@@ -24,7 +24,7 @@ class Event(BaseModel):
 
     id: str  # unique, stable across republish
     source: str  # adapter identity, e.g. "central/adapters/nws"
-    category: str  # e.g. "wx.alert.severe_thunderstorm_warning"
+    category: str  # e.g. "wx.alert.severe_thunderstorm_warning" or "fire.hotspot.viirs_snpp.high"
     time: datetime  # event-time UTC, not processing-time
     expires: datetime | None = None
     severity: int | None = None  # 0..4 or None for "Unknown"
@@ -32,19 +32,30 @@ class Event(BaseModel):
     data: dict[str, Any]  # adapter-specific payload
 
 
-def subject_for_event(ev: Event, prefix: str = "central.wx") -> str:
+def subject_for_event(ev: Event) -> str:
     """
-    Compute the NATS subject for an alert-style event.
+    Compute the NATS subject for an event based on its category.
 
-    For weather alerts the subject is:
+    Dispatch by category prefix:
+    - fire.*: returns central.<category> directly
+    - wx.*: uses weather alert subject logic
+
+    Weather alert subjects:
       central.wx.alert.us.<state_lower>.county.<county_lower>
     or
       central.wx.alert.us.<state_lower>.zone.<zone_lower>
     based on whether the primary_region encodes a county or a zone.
 
-    If primary_region is None or unparseable, returns:
-      central.wx.alert.us.unknown
+    Fire hotspot subjects:
+      central.fire.hotspot.<satellite>.<confidence>
     """
+    # Fire events: subject is just central.<category>
+    if ev.category.startswith("fire."):
+        return f"central.{ev.category}"
+
+    # Weather events: use geo-based subject logic
+    prefix = "central.wx"
+
     if ev.geo.primary_region is None:
         return f"{prefix}.alert.us.unknown"