Add new activity events and enhance ActivityBloc for better state management

- Introduced LoadTripActivitiesPreservingSearch event to load trip activities while preserving search results.
- Added RemoveFromSearchResults and AddActivityAndRemoveFromSearch events for improved activity handling.
- Updated ActivitiesPage to show loading dialog during activity addition and provide user feedback.
- Increased maxResults for activity search to load more activities.

lib/blocs/activity/activity_event.dart

@@ -19,6 +19,16 @@ class LoadActivities extends ActivityEvent {
   List<Object> get props => [tripId];
 }
 
+/// Event to load trip activities without resetting search results
+class LoadTripActivitiesPreservingSearch extends ActivityEvent {
+  final String tripId;
+
+  const LoadTripActivitiesPreservingSearch(this.tripId);
+
+  @override
+  List<Object> get props => [tripId];
+}
+
 /// Event to search activities using Google Places API
 class SearchActivities extends ActivityEvent {
   final String tripId;
@@ -194,4 +204,28 @@ class RestoreCachedSearchResults extends ActivityEvent {
 
   @override
   List<Object?> get props => [searchResults];
+}
+
+/// Event to remove an activity from search results
+class RemoveFromSearchResults extends ActivityEvent {
+  final String activityId;
+
+  const RemoveFromSearchResults({required this.activityId});
+
+  @override
+  List<Object> get props => [activityId];
+}
+
+/// Event to add an activity and remove it from search results in one action
+class AddActivityAndRemoveFromSearch extends ActivityEvent {
+  final Activity activity;
+  final String googleActivityId;
+
+  const AddActivityAndRemoveFromSearch({
+    required this.activity,
+    required this.googleActivityId,
+  });
+
+  @override
+  List<Object> get props => [activity, googleActivityId];
 }