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

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

lib/screens/search_screen.dart

@@ -106,8 +106,24 @@ class _SearchScreenState extends State<SearchScreen> {
     });
   }
 
+  /// Pop with a structured result so home_screen can update both the display
+  /// label AND the pincode / GPS coordinates used for API filtering.
+  void _selectWithPincode(String label, {String? pincode}) {
+    Navigator.of(context).pop(<String, dynamic>{
+      'label': label,
+      'pincode': pincode ?? 'all',
+    });
+  }
+
   void _selectAndClose(String location) {
-    Navigator.of(context).pop(location);
+    // Legacy path for plain strings — wrap in structured map.
+    // Tries to look up a pincode from the database for the given city name.
+    final match = _locationDb.cast<_LocationItem?>().firstWhere(
+      (loc) => loc!.city.toLowerCase() == location.toLowerCase() ||
+               loc.displayTitle.toLowerCase() == location.toLowerCase(),
+      orElse: () => null,
+    );
+    _selectWithPincode(location, pincode: match?.pincode);
   }
 
   Future<void> _useCurrentLocation() async {
@@ -122,13 +138,14 @@ class _SearchScreenState extends State<SearchScreen> {
       if (permission == LocationPermission.deniedForever || permission == LocationPermission.denied) {
         if (mounted) {
           ScaffoldMessenger.of(context).showSnackBar(const SnackBar(content: Text('Location permission denied')));
-          Navigator.of(context).pop('Current Location');
+          Navigator.of(context).pop(<String, dynamic>{'label': 'Current Location', 'pincode': 'all'});
         }
         return;
       }
 
       final pos = await Geolocator.getCurrentPosition(desiredAccuracy: LocationAccuracy.best);
 
+      String label = 'Current Location';
       try {
         final placemarks = await placemarkFromCoordinates(pos.latitude, pos.longitude);
         if (placemarks.isNotEmpty) {
@@ -137,17 +154,24 @@ class _SearchScreenState extends State<SearchScreen> {
           if ((p.subLocality ?? '').isNotEmpty) parts.add(p.subLocality!);
           if ((p.locality ?? '').isNotEmpty) parts.add(p.locality!);
           if ((p.subAdministrativeArea ?? '').isNotEmpty) parts.add(p.subAdministrativeArea!);
-          final label = parts.isNotEmpty ? parts.join(', ') : 'Current Location';
-          if (mounted) Navigator.of(context).pop(label);
-          return;
+          if (parts.isNotEmpty) label = parts.join(', ');
         }
       } catch (_) {}
 
-      if (mounted) Navigator.of(context).pop('Current Location');
+      if (mounted) {
+        // Return lat/lng so home_screen can use haversine filtering
+        Navigator.of(context).pop(<String, dynamic>{
+          'label': label,
+          'pincode': 'all',
+          'lat': pos.latitude,
+          'lng': pos.longitude,
+        });
+      }
+      return;
     } catch (e) {
       if (mounted) {
         ScaffoldMessenger.of(context).showSnackBar(SnackBar(content: Text(userFriendlyError(e))));
-        Navigator.of(context).pop('Current Location');
+        Navigator.of(context).pop(<String, dynamic>{'label': 'Current Location', 'pincode': 'all'});
       }
     } finally {
       if (mounted) setState(() => _loadingLocation = false);
@@ -320,7 +344,7 @@ class _SearchScreenState extends State<SearchScreen> {
                         subtitle: loc.pincode != null && loc.pincode!.isNotEmpty
                             ? Text(loc.pincode!, style: TextStyle(color: Colors.grey[500], fontSize: 13))
                             : null,
-                        onTap: () => _selectAndClose(loc.returnValue),
+                        onTap: () => _selectWithPincode(loc.displayTitle, pincode: loc.pincode),
                       );
                     },
                   ),