fix(polls): prevent jarring reload when switching to My Trips tab

- Only load polls once on initial view appearance, not every tab switch
- Only show spinner when there's no existing data (first load)
- Subsequent refreshes update content in place without showing spinner

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/Features/Home/Views/HomeView.swift

@@ -411,6 +411,7 @@ struct SavedTripsListView: View {
 
     @State private var polls: [TripPoll] = []
     @State private var isLoadingPolls = false
+    @State private var hasLoadedPolls = false
     @State private var showCreatePoll = false
     @State private var selectedPoll: TripPoll?
 
@@ -437,6 +438,8 @@ struct SavedTripsListView: View {
         }
         .themedBackground()
         .task {
+            guard !hasLoadedPolls else { return }
+            hasLoadedPolls = true
             await loadPolls()
         }
         .refreshable {
@@ -474,7 +477,7 @@ struct SavedTripsListView: View {
                 }
             }
 
-            if isLoadingPolls {
+            if isLoadingPolls && polls.isEmpty {
                 ProgressView()
                     .frame(maxWidth: .infinity, alignment: .center)
                     .padding()