refactor(server): fold airports and distance, drop the boot-time backfill cycle (#1834)

Two thirds of be-weather-airports-fold. weatherService (513 LOC, a process
cache and a setInterval at import) is left for its own PR.

airportService split along the line that was already there. The dataset lookup
touches no database — it reads one JSON file and keeps it in memory — and both
MCP registrars call it from outside the container, so findByIata/searchAirports
are free functions in nest/airports/airports.data.ts. backfillFlightEndpoints
needs the connection and became a method on AirportsService.

That backfill was the interesting part. db/database.ts ran it at module eval
through a bare require() back into services/, so the module graph closed a cycle
that only held because `db` happened to be initialised by the time the require
resolved. It runs in onApplicationBootstrap now: it repairs rows, nothing boots
on it, and the container is fully built by then.

The cycle had a visible cost. tests/setup.console-noise.ts carried a suppression
for `Cannot find module '../services/airportService'`, because vitest's
transform pipeline could not resolve that require at all — it fired in roughly
sixty test files. That suppression is now narrowed to the only case left: an e2e
TestingModule whose fixture DB has no reservations table.

distanceService split the same way: haversineKm is arithmetic and moved to
common/geo.ts; getFlightDistanceKm reads the database and became a private
method on AuthService, its only caller.

AirportsModule imports DatabaseModule explicitly. @Global only reaches modules
that are in the graph, and the airports e2e builds its container from
AirportsModule alone — exactly the trap the nest README now documents.

The search ranking gets its first direct tests. It sat in services/, outside the
coverage gate, and only ever ran incidentally through the route; moving it into
src/nest made the gap measurable (16% branches). The ten cases pin the scoring
ladder — exact IATA short-circuit, ICAO over prefix, IATA prefix over city
prefix, city prefix over substring — and the missing-dataset fallback, which no
test had reached. 90% branches now.

server/src/db/database.ts

@@ -167,12 +167,6 @@ function isOwner(tripId: number | string, userId: number): boolean {
   return !!db.prepare('SELECT id FROM trips WHERE id = ? AND user_id = ?').get(tripId, userId);
 }
 
-try {
-  const { backfillFlightEndpoints } = require('../services/airportService');
-  backfillFlightEndpoints();
-} catch (err) {
-  console.error('[DB] Flight endpoint backfill failed:', err);
-}
 
 export { db, closeDb, reinitialize, getPlaceWithTags, canAccessTrip, isOwner };
 export type { TripAccess, PlaceWithTags };