feat(polls): add DeepLinkHandler and test mock helpers

- Extract deep link handling into dedicated DeepLinkHandler service
- Add MockData+Polls.swift with reusable test mocks for Trip, TripStop,
  TripPoll, PollVote, and PollResults
- Update SportsTimeApp to use DeepLinkHandler.shared
- Add error alert for deep link failures

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

SportsTime/SportsTimeApp.swift

@@ -81,7 +81,7 @@ struct BootstrappedContentView: View {
     @State private var bootstrapError: Error?
     @State private var hasCompletedInitialSync = false
     @State private var showOnboardingPaywall = false
-    @State private var pollShareCode: String?
+    @State private var deepLinkHandler = DeepLinkHandler.shared
 
     private var shouldShowOnboardingPaywall: Bool {
         !UserDefaults.standard.bool(forKey: "hasSeenOnboardingPaywall") && !StoreManager.shared.isPro
@@ -103,11 +103,16 @@ struct BootstrappedContentView: View {
                         OnboardingPaywallView(isPresented: $showOnboardingPaywall)
                             .interactiveDismissDisabled()
                     }
-                    .sheet(item: $pollShareCode) { code in
+                    .sheet(item: $deepLinkHandler.pendingPollShareCode) { code in
                         NavigationStack {
                             PollDetailView(shareCode: code)
                         }
                     }
+                    .alert("Error", isPresented: .constant(deepLinkHandler.error != nil)) {
+                        Button("OK") { deepLinkHandler.clearPending() }
+                    } message: {
+                        Text(deepLinkHandler.error?.localizedDescription ?? "")
+                    }
                     .onAppear {
                         if shouldShowOnboardingPaywall {
                             showOnboardingPaywall = true
@@ -119,7 +124,7 @@ struct BootstrappedContentView: View {
             await performBootstrap()
         }
         .onOpenURL { url in
-            handleDeepLink(url)
+            deepLinkHandler.handleURL(url)
         }
         .onChange(of: scenePhase) { _, newPhase in
             switch newPhase {
@@ -204,18 +209,6 @@ struct BootstrappedContentView: View {
         }
     }
 
-    // MARK: - Deep Link Handling
-
-    private func handleDeepLink(_ url: URL) {
-        // Handle sportstime://poll/{code} deep links
-        guard url.scheme == "sportstime",
-              url.host == "poll",
-              let code = url.pathComponents.dropFirst().first,
-              code.count == 6
-        else { return }
-
-        pollShareCode = code.uppercased()
-    }
 }
 
 // MARK: - String Identifiable for Sheet