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>