Copy the airports generation script to buiild

[cwdaniel]

Summary

• Fix three code review issues: ICAO case normalization, stale watchlist cleanup, and tile-boundary sampling
• Fix airports.json missing from Docker image causing situation-api to crash-loop
• Fix airports unit test to not depend on generated data file (fixes CI)

Changes

• ICAO normalization (src/situation/ws/aviation.ts): Normalize watchlist ICAOs to uppercase before storing subscriptions, so downstream Redis keys (situation:airport:KORD,
  sismember) match regardless of client casing
• Stale watchlist cleanup (src/situation/index.ts): syncWatchlist now diffs the Redis watchlist against active WS subscriptions and calls removeFromWatchlist for airports
  with no connected clients, preventing unbounded growth
• Tile boundary sampling (src/situation/sampling/route-sampler.ts): When a neighborhood sample crosses a tile boundary, load adjacent tiles and sample from the correct one
  instead of discarding out-of-bounds pixels. Fast path (single tile) preserved for the common case
• Docker build (docker/Dockerfile): Generate airports.json at build time via generate-airports.ts so the situation-api container can start
• CI fix (tests/unit/situation/airports.test.ts): Mock bundled airport data instead of reading from filesystem, so tests pass without the generated file