feat(sharing): implement unified sharing system for social media

Replace old ProgressCardGenerator with protocol-based sharing architecture
supporting trips, achievements, and stadium progress. Features 8 color
themes, Instagram Stories optimization (1080x1920), and reusable card
components with map snapshots.

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

SportsTime/Features/Trip/Views/TripDetailView.swift

@@ -18,9 +18,7 @@ struct TripDetailView: View {
     @State private var showProPaywall = false
     @State private var selectedDay: ItineraryDay?
     @State private var showExportSheet = false
-    @State private var showShareSheet = false
     @State private var exportURL: URL?
-    @State private var shareURL: URL?
     @State private var isExporting = false
     @State private var exportProgress: PDFAssetPrefetcher.PrefetchProgress?
     @State private var mapCameraPosition: MapCameraPosition = .automatic
@@ -63,12 +61,8 @@ struct TripDetailView: View {
         .toolbarBackground(Theme.cardBackground(colorScheme), for: .navigationBar)
         .toolbar {
             ToolbarItemGroup(placement: .primaryAction) {
-                Button {
-                    shareTrip()
-                } label: {
-                    Image(systemName: "square.and.arrow.up")
-                        .foregroundStyle(Theme.warmOrange)
-                }
+                ShareButton(trip: trip, style: .icon)
+                    .foregroundStyle(Theme.warmOrange)
 
                 Button {
                     if StoreManager.shared.isPro {
@@ -94,13 +88,6 @@ struct TripDetailView: View {
                 ShareSheet(items: [url])
             }
         }
-        .sheet(isPresented: $showShareSheet) {
-            if let url = shareURL {
-                ShareSheet(items: [url])
-            } else {
-                ShareSheet(items: [trip.name, trip.formattedDateRange])
-            }
-        }
         .sheet(isPresented: $showProPaywall) {
             PaywallView()
         }
@@ -523,11 +510,6 @@ struct TripDetailView: View {
         isExporting = false
     }
 
-    private func shareTrip() {
-        shareURL = exportService.shareTrip(trip)
-        showShareSheet = true
-    }
-
     private func toggleSaved() {
         if isSaved {
             unsaveTrip()