- Rewrite airport search to use priority buckets instead of simple
append: exact IATA → IATA prefix → city prefix → city contains →
name prefix → name contains → country match. This ensures BER
appears before Berlin-Schönefeld when typing "BER".
- Add _MISSING_AIRPORTS patch list to get_airport_data() so airports
absent from the OpenFlights dataset (e.g. BER opened Nov 2020,
IST new Istanbul airport) are included at runtime.
- Deduplicate results via seen-set to avoid duplicate entries.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>