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-frontend/lib/useVessels.ts

@@ -0,0 +1,53 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import { collection, onSnapshot, query, where, FirestoreError } from "firebase/firestore";
+import { onAuthStateChanged } from "firebase/auth";
+import { db, auth } from "@/lib/firebase";
+import { useAuth } from "@/components/AuthProvider";
+import type { VesselTrack } from "@/lib/types";
+
+// Same shape as useAircraft — `vessels` is a live snapshot (one per mmsi,
+// overwritten on every sighting, node-26#9), nothing prunes a doc when a
+// vessel goes out of range, so staleness is filtered client-side. AIS
+// position reports are much less frequent than ADS-B (minutes, not
+// seconds), so this window is longer than useAircraft's.
+const STALE_AFTER_MS = 10 * 60 * 1000;
+
+export function useVessels() {
+  const [vessels, setVessels] = useState<VesselTrack[]>([]);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+  const { orgId } = useAuth();
+
+  useEffect(() => {
+    let unsubFirestore: (() => void) | undefined;
+
+    const unsubAuth = onAuthStateChanged(auth, (user) => {
+      if (unsubFirestore) { unsubFirestore(); unsubFirestore = undefined; }
+
+      if (!user || !orgId) {
+        setVessels([]);
+        setLoading(false);
+        return;
+      }
+
+      const q = query(collection(db, "vessels"), where("org_id", "==", orgId));
+      unsubFirestore = onSnapshot(q, (snap) => {
+        const now = Date.now();
+        const fresh = snap.docs
+          .map((d) => d.data() as VesselTrack)
+          .filter((v) => now - new Date(v.last_seen).getTime() < STALE_AFTER_MS);
+        setVessels(fresh);
+        setLoading(false);
+      }, (err: FirestoreError) => { console.error("useVessels:", err); setError(err.message); setLoading(false); });
+    });
+
+    return () => {
+      unsubAuth();
+      if (unsubFirestore) unsubFirestore();
+    };
+  }, [orgId]);
+
+  return { vessels, loading, error };
+}