fix: improve airport search ranking and add missing modern airports

- 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>

flight-comparator/api_server.py

@@ -880,40 +880,56 @@ async def search_airports(
         raise HTTPException(status_code=500, detail=f"Failed to load airport data: {e}")
 
     query = q.lower().strip()
-    results = []
 
-    # Search all airports
+    # Priority buckets — higher bucket = shown first
+    p0_exact_iata: list[Airport] = []    # IATA == query exactly  (e.g. "BER")
+    p1_iata_prefix: list[Airport] = []   # IATA starts with query (e.g. "BE" → BER)
+    p2_city_prefix: list[Airport] = []   # city starts with query (e.g. "ber" → Berlin)
+    p3_city_contains: list[Airport] = [] # city contains query
+    p4_name_prefix: list[Airport] = []   # name starts with query
+    p5_name_contains: list[Airport] = [] # name contains query
+    p6_country: list[Airport] = []       # country code contains query
+    seen: set[str] = set()
+
     for airport in airports_data:
-        # Skip invalid airport data (data quality issues in OpenFlights dataset)
         try:
-            # Search in IATA code (exact match prioritized)
+            iata_l = airport['iata'].lower()
-            if airport['iata'].lower() == query:
+            city_l = airport.get('city', '').lower()
-                results.insert(0, Airport(**airport))  # Exact match at top
+            name_l = airport['name'].lower()
+            country_l = airport.get('country', '').lower()
+
+            if iata_l in seen:
                 continue
 
-            # Search in IATA code (partial match)
+            obj = Airport(**airport)
-            if query in airport['iata'].lower():
+
-                results.append(Airport(**airport))
+            if iata_l == query:
+                p0_exact_iata.append(obj)
+            elif iata_l.startswith(query):
+                p1_iata_prefix.append(obj)
+            elif city_l.startswith(query):
+                p2_city_prefix.append(obj)
+            elif query in city_l:
+                p3_city_contains.append(obj)
+            elif name_l.startswith(query):
+                p4_name_prefix.append(obj)
+            elif query in name_l:
+                p5_name_contains.append(obj)
+            elif query in country_l:
+                p6_country.append(obj)
+            else:
                 continue
 
-            # Search in city name
+            seen.add(iata_l)
-            if query in airport.get('city', '').lower():
-                results.append(Airport(**airport))
-                continue
-
-            # Search in airport name
-            if query in airport['name'].lower():
-                results.append(Airport(**airport))
-                continue
-
-            # Search in country code
-            if query in airport['country'].lower():
-                results.append(Airport(**airport))
-                continue
         except Exception:
             # Skip airports with invalid data (e.g., invalid IATA codes like 'DU9')
             continue
 
+    results = (
+        p0_exact_iata + p1_iata_prefix + p2_city_prefix +
+        p3_city_contains + p4_name_prefix + p5_name_contains + p6_country
+    )
+
     # Calculate pagination
     total = len(results)
     total_pages = math.ceil(total / limit) if total > 0 else 0
@@ -1607,6 +1623,13 @@ app.include_router(router_v1)
 # Helper Functions
 # =============================================================================
 
+# Airports missing from the OpenFlights dataset (opened/renamed after dataset freeze)
+_MISSING_AIRPORTS = [
+    {'iata': 'BER', 'name': 'Berlin Brandenburg Airport', 'city': 'Berlin', 'country': 'DE'},
+    {'iata': 'IST', 'name': 'Istanbul Airport', 'city': 'Istanbul', 'country': 'TR'},
+]
+
+
 @lru_cache(maxsize=1)
 def get_airport_data():
     """
@@ -1637,6 +1660,19 @@ def get_airport_data():
                 'longitude': airport.get('lon', 0.0),
             })
 
+    # Patch in modern airports missing from the OpenFlights dataset
+    existing_iatas = {a['iata'] for a in airports}
+    for extra in _MISSING_AIRPORTS:
+        if extra['iata'] not in existing_iatas:
+            airports.append({
+                'iata': extra['iata'],
+                'name': extra['name'],
+                'city': extra['city'],
+                'country': extra['country'],
+                'latitude': 0.0,
+                'longitude': 0.0,
+            })
+
     return airports