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/Progress/Views/AchievementsListView.swift

@@ -36,6 +36,20 @@ struct AchievementsListView: View {
         }
         .themedBackground()
         .navigationTitle("Achievements")
+        .toolbar {
+            ToolbarItem(placement: .topBarTrailing) {
+                if !earnedAchievements.isEmpty {
+                    ShareButton(
+                        content: AchievementCollectionContent(
+                            achievements: earnedAchievements,
+                            year: Calendar.current.component(.year, from: Date())
+                        ),
+                        style: .icon
+                    )
+                    .foregroundStyle(Theme.warmOrange)
+                }
+            }
+        }
         .task {
             await loadAchievements()
         }
@@ -184,6 +198,10 @@ struct AchievementsListView: View {
         }
     }
 
+    private var earnedAchievements: [AchievementProgress] {
+        achievements.filter { $0.isEarned }
+    }
+
     private var filteredAchievements: [AchievementProgress] {
         let filtered: [AchievementProgress]