fix: enrich route destination names from airport DB when not stored

Specific-airports mode scans never resolved full airport names — they
stored the IATA code as destination_name. Fixed in two places:

- airports.py: add lookup_airport(iata) cached helper
- api_server.py: enrich destination_name/city on the fly in the routes
  endpoint when the stored value equals the IATA code (fixes all past scans)
- scan_processor.py: resolve airport names at scan time in specific-airports
  mode using lookup_airport (fixes future scans at the DB level)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

flight-comparator/api_server.py

@@ -1430,7 +1430,8 @@ async def get_scan_routes(
         rows = cursor.fetchall()
         conn.close()
 
-        # Convert to Route models
+        # Convert to Route models, enriching name/city from airport DB when missing
+        lookup = _iata_lookup()
         routes = []
         for row in rows:
             # Parse airlines JSON
@@ -1439,12 +1440,22 @@ async def get_scan_routes(
             except:
                 airlines = []
 
+            dest = row[2]
+            dest_name = row[3] or dest
+            dest_city = row[4] or ''
+
+            # If name was never resolved (stored as IATA code), look it up now
+            if dest_name == dest:
+                airport = lookup.get(dest, {})
+                dest_name = airport.get('name', dest)
+                dest_city = airport.get('city', dest_city)
+
             routes.append(Route(
                 id=row[0],
                 scan_id=row[1],
-                destination=row[2],
-                destination_name=row[3],
-                destination_city=row[4],
+                destination=dest,
+                destination_name=dest_name,
+                destination_city=dest_city,
                 flight_count=row[5],
                 airlines=airlines,
                 min_price=row[7],
@@ -1712,6 +1723,12 @@ def get_airport_data():
     return airports
 
 
+@lru_cache(maxsize=1)
+def _iata_lookup() -> dict:
+    """Return {iata: airport_dict} built from get_airport_data(). Cached."""
+    return {a['iata']: a for a in get_airport_data()}
+
+
 if __name__ == "__main__":
     import uvicorn
     uvicorn.run(app, host="0.0.0.0", port=8000)