ADS-B map: altitude-colored aircraft icons + click-to-show flight trail

Icons were 16px accent-colored glyphs, indistinguishable from OSM's own
airport symbols. Now a 30px outlined airliner silhouette filled on
tar1090/ADS-B Exchange's altitude hue ramp, with a callsign/altitude
hover tooltip; the selected aircraft grows and gets a white outline.

Clicking an aircraft draws the path heard so far, segment-colored by
altitude. c2-core writes one point per position change to
aircraft/{icao}/positions (deduped in-process, writes now concurrent);
points carry expire_at and a TTL fieldOverride deletes them after ~24h.
Trail reads are gated on the parent aircraft doc's org via get(), so the
query needs no org filter or composite index. The latest stretch without
a 20-min gap counts as the current flight.

Verified: c2-core pytest 479 passed; frontend tsc --noEmit clean (node:20
container on radio-box).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

infra/firestore/firestore.rules

@@ -98,6 +98,14 @@ service cloud.firestore {
     match /aircraft/{icao} {
       allow read: if docInMyOrg();
       allow write: if false;
+
+      // Flight trail points. Org is checked against the PARENT aircraft doc
+      // (one get() per query) so the map can query a trail by time alone,
+      // without an org_id filter and the composite index that would need.
+      match /positions/{pointId} {
+        allow read: if inOrg(get(/databases/$(database)/documents/aircraft/$(icao)).data.org_id);
+        allow write: if false;
+      }
     }
 
     match /vessels/{mmsi} {