feat(squawk): carry emergencySource + observation time into analyst records

Review on #856 (kvnloo): the analyst projection flattened a 7700 squawk and
the readsb ADS-B emergency field into the same emergency/emergencyKind pair.

- mapAnalystRecord (flights, military) adds emergencySource ('squawk' |
  'ads-b' | null, from aircraftEmergency().source), emergencyBroadcast (new
  pure emergencyBroadcastPhrase: "broadcasting squawk 7700 (general
  emergency)" vs "ADS-B reports general emergency") and observedAtMs (the
  record's lastContactEpochMs: last transponder message, epoch ms).
- emergencySource is a queryable analyst text field; the voice payload passes
  it and emergencyBroadcast through, and observedAtMs only for aircraft with
  a status. Tool description asks the model to narrate with the phrase.
- Source-to-analyst fixture test: OpenSky 7700 vs adsb.lol emergency=general
  on squawk 1200 differ in provenance and timestamp; filterable by source.
- Voice tool-payload pins re-derived for the additive description change.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

src/data/flights.test.mjs

@@ -74,6 +74,9 @@ test('flights analyst record: full record maps every contract field', () => {
     squawk: null,
     emergency: false,
     emergencyKind: null,
+    emergencySource: null,
+    emergencyBroadcast: null,
+    observedAtMs: null,
     routeOrigin: 'AUS',
     routeDestination: 'LAX',
   });