Wire AIS end to end: telemetry ingestion + live map overlay

node-26#9, same shape as the ADS-B commit. Adds POST /telemetry/ais
(same node-key auth, same org_id-stamped upsert-by-key pattern, this time
by mmsi into a new `vessels` collection) and its docInMyOrg() firestore
rule. Frontend gets useVessels() (mirrors useAircraft(), longer staleness
window since AIS position reports are minutes apart, not seconds) and an
opt-in "Vessels" map overlay.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

drb-c2-core/app/models.py

@@ -85,6 +85,20 @@ class AircraftTrack(BaseModel):
     last_seen: datetime
 
 
+class VesselTrack(BaseModel):
+    """Live AIS position, one doc per mmsi. Same live-snapshot shape as
+    AircraftTrack — overwritten on every sighting (see node-26#9)."""
+    mmsi: str
+    org_id: Optional[str] = None
+    node_id: str
+    name: Optional[str] = None
+    lat: Optional[float] = None
+    lon: Optional[float] = None
+    speed_kt: Optional[float] = None
+    heading_deg: Optional[float] = None
+    last_seen: datetime
+
+
 class CommandPayload(BaseModel):
     action: str                      # discord_join / discord_leave / op25_restart
     guild_id: Optional[str] = None