feat(ui): add sport backgrounds to share cards, achievement filtering, and wizard validation

- Add ShareCardSportBackground with floating sport icons for share cards
- Share cards now show sport-specific backgrounds (single or multiple sports)
- Achievement collection share respects sport filter selection
- Add ability to share individual achievements from detail sheet
- Trip wizard ReviewStep highlights missing required fields in red
- Add FieldValidation model to TripWizardViewModel

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

SportsTime/Features/Progress/Views/AchievementsListView.swift

@@ -38,11 +38,27 @@ struct AchievementsListView: View {
         .navigationTitle("Achievements")
         .toolbar {
             ToolbarItem(placement: .topBarTrailing) {
-                if !earnedAchievements.isEmpty {
+                // Share only achievements matching current filter
+                let achievementsToShare = selectedSport != nil
+                    ? filteredAchievements.filter { $0.isEarned }
+                    : earnedAchievements
+
+                // Collect sports for background: single sport if filtered, all sports from achievements if "All"
+                let sportsForBackground: Set<Sport> = {
+                    if let sport = selectedSport {
+                        return [sport]
+                    }
+                    // Extract all unique sports from earned achievements
+                    return Set(achievementsToShare.compactMap { $0.definition.sport })
+                }()
+
+                if !achievementsToShare.isEmpty {
                     ShareButton(
                         content: AchievementCollectionContent(
-                            achievements: earnedAchievements,
-                            year: Calendar.current.component(.year, from: Date())
+                            achievements: achievementsToShare,
+                            year: Calendar.current.component(.year, from: Date()),
+                            sports: sportsForBackground,
+                            filterSport: selectedSport
                         ),
                         style: .icon
                     )
@@ -573,6 +589,16 @@ struct AchievementDetailSheet: View {
                 ToolbarItem(placement: .cancellationAction) {
                     Button("Done") { dismiss() }
                 }
+
+                if achievement.isEarned {
+                    ToolbarItem(placement: .primaryAction) {
+                        ShareButton(
+                            content: AchievementSpotlightContent(achievement: achievement),
+                            style: .icon
+                        )
+                        .foregroundStyle(completedGold)
+                    }
+                }
             }
         }
     }