fix: LOC — location filter never applied to event API calls

Root cause: SearchScreen popped with a plain city label string; the
pincode was available in search results but discarded. home_screen only
saved the display label to prefs and never updated the 'pincode' key,
so every API call always sent {pincode:'all'} regardless of selection.

GPS path had the same issue — lat/lng were obtained but thrown away
after reverse-geocoding; only the label was passed back.

Fix:
- SearchScreen now pops with Map<String,dynamic> {label, pincode,
  lat?, lng?} instead of a plain String
- Pincode results return their pincode; GPS returns actual coordinates;
  popular city chips look up the first matching pincode from the
  Kerala pincodes DB (fallback 'all' if not found)
- home_screen._openLocationSearch() saves pincode + lat/lng to prefs
  and updates _pincode/_userLat/_userLng in state
- home_screen._loadUserDataAndEvents() prefers getEventsByLocation
  (haversine) when GPS coords are saved, falls back to getEventsByPincode
- EventsService gains getEventsByLocation(lat, lng) which sends
  latitude/longitude/radius_km to the existing Django haversine endpoint
  and auto-expands radius 10→25→50→100 km until ≥ 6 events found

lib/screens/home_screen.dart

@@ -37,6 +37,8 @@ class _HomeScreenState extends State<HomeScreen> with SingleTickerProviderStateM
   String _username = '';
   String _location = '';
   String _pincode = 'all';
+  double? _userLat;
+  double? _userLng;
 
   final EventsService _eventsService = EventsService();
 
@@ -104,12 +106,17 @@ class _HomeScreenState extends State<HomeScreen> with SingleTickerProviderStateM
       _location = storedLocation;
     }
     _pincode = prefs.getString('pincode') ?? 'all';
+    _userLat = prefs.getDouble('user_lat');
+    _userLng = prefs.getDouble('user_lng');
 
     try {
-      // Fetch types and events in parallel for faster loading
+      // Fetch types and events in parallel for faster loading.
+      // Prefer haversine (lat/lng) when GPS coords are available; fall back to pincode.
       final results = await Future.wait([
         _events_service_getEventTypesSafe(),
-        _events_service_getEventsSafe(_pincode),
+        (_userLat != null && _userLng != null)
+            ? _events_service_getEventsByLocationSafe(_userLat!, _userLng!)
+            : _events_service_getEventsSafe(_pincode),
       ]);
       final types = results[0] as List<EventTypeModel>;
       final events = results[1] as List<EventModel>;
@@ -171,6 +178,15 @@ class _HomeScreenState extends State<HomeScreen> with SingleTickerProviderStateM
     }
   }
 
+  Future<List<EventModel>> _events_service_getEventsByLocationSafe(double lat, double lng) async {
+    try {
+      return await _eventsService.getEventsByLocation(lat, lng);
+    } catch (_) {
+      // Fallback to all events if location-based fetch fails
+      return _events_service_getEventsSafe('all');
+    }
+  }
+
   Future<void> _refresh() async {
     await _loadUserDataAndEvents();
   }
@@ -277,12 +293,31 @@ class _HomeScreenState extends State<HomeScreen> with SingleTickerProviderStateM
       transitionDuration: const Duration(milliseconds: 220),
     ));
 
-    if (selected != null && selected is String) {
+    if (selected != null && selected is Map) {
+      final label = (selected['label'] as String?) ?? 'Current Location';
+      final pincode = (selected['pincode'] as String?) ?? 'all';
+      final lat = selected['lat'] as double?;
+      final lng = selected['lng'] as double?;
+
       final prefs = await SharedPreferences.getInstance();
-      await prefs.setString('location', selected);
-      setState(() {
-        _location = selected;
-      });
+      await prefs.setString('location', label);
+      await prefs.setString('pincode', pincode);
+      if (lat != null && lng != null) {
+        await prefs.setDouble('user_lat', lat);
+        await prefs.setDouble('user_lng', lng);
+      } else {
+        await prefs.remove('user_lat');
+        await prefs.remove('user_lng');
+      }
+
+      if (mounted) {
+        setState(() {
+          _location = label;
+          _pincode = pincode;
+          _userLat = lat;
+          _userLng = lng;
+        });
+      }
       await _refresh();
     }
   }