Fix theme selection bug and update onboarding with AppTheme picker

- Change Theme enum from Int to String raw values to fix theme selection bug
- Replace OnboardingStyle icon/color pickers with unified AppTheme grid
- Remove visible text labels from voting layouts while keeping accessibility labels (WCAG 2.1 AA compliant)
- Update widget voting views to use icons only with proper accessibility support
- Consolidate app icons to single unified icon set

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Shared/Models/Theme.swift

@@ -11,12 +11,23 @@ struct ThemeConstants {
     static let iconSize: CGFloat = 50
 }
 
-enum Theme: Int, CaseIterable {
-    case system
-    case iFeel
-    case dark
-    case light
-    
+enum Theme: String, CaseIterable {
+    case system = "system"
+    case iFeel = "iFeel"
+    case dark = "dark"
+    case light = "light"
+
+    // Legacy Int-based init for backwards compatibility with existing UserDefaults data
+    init?(legacyIntValue: Int) {
+        switch legacyIntValue {
+        case 0: self = .system
+        case 1: self = .iFeel
+        case 2: self = .dark
+        case 3: self = .light
+        default: return nil
+        }
+    }
+
     var title: String {
         switch self {
         case .system:

Shared/Models/UserDefaultsStore.swift

@@ -248,11 +248,29 @@ class UserDefaultsStore {
     }
     
     static func theme() -> Theme {
-        if let data = GroupUserDefaults.groupDefaults.object(forKey: UserDefaultsStore.Keys.theme.rawValue) as? Int,
-           let model = Theme.init(rawValue: data) {
+        // Try String value first (new format)
+        if let stringValue = GroupUserDefaults.groupDefaults.object(forKey: UserDefaultsStore.Keys.theme.rawValue) as? String,
+           let model = Theme(rawValue: stringValue) {
             return model
-        } else {
-            return Theme.system
+        }
+        // Fall back to Int value (legacy format for existing users)
+        if let intValue = GroupUserDefaults.groupDefaults.object(forKey: UserDefaultsStore.Keys.theme.rawValue) as? Int,
+           let model = Theme(legacyIntValue: intValue) {
+            // Migrate to new String format
+            GroupUserDefaults.groupDefaults.set(model.rawValue, forKey: UserDefaultsStore.Keys.theme.rawValue)
+            return model
+        }
+        return Theme.system
+    }
+
+    /// Call this on app launch to migrate any legacy Int-based theme values to String format
+    static func migrateThemeIfNeeded() {
+        // Check if we have an Int value stored (legacy format)
+        if let intValue = GroupUserDefaults.groupDefaults.object(forKey: UserDefaultsStore.Keys.theme.rawValue) as? Int,
+           let model = Theme(legacyIntValue: intValue) {
+            // Migrate to new String format
+            GroupUserDefaults.groupDefaults.set(model.rawValue, forKey: UserDefaultsStore.Keys.theme.rawValue)
+            GroupUserDefaults.groupDefaults.synchronize()
         }
     }