fix(docker): include server/data/airports.json in the image

The existing 'data' entry in .dockerignore hid the committed
airports.json snapshot from the build context, so every Docker
deployment ended up without it. The airport service then logged the
"missing" warning and the autocomplete silently returned no results —
the dropdown flashed a loading spinner and disappeared. Add an
exception that keeps the SQLite DB, logs and tmp excluded but lets
the airports snapshot through.

.dockerignore

@@ -3,6 +3,7 @@ client/node_modules
 server/node_modules
 client/dist
 data
+!server/data/airports.json
 uploads
 .git
 .github