feat: in-app dark mode toggle (System / Light / Dark)

- AppearanceManager with UserDefaults persistence
- Three modes: System (follows iOS), Light, Dark
- Toggle in Home screen profile menu under "Appearance"
- Applied via .preferredColorScheme at app root
- Persists across app launches

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ios/Platform/Platform.xcodeproj/project.pbxproj

@@ -12,6 +12,7 @@
 		A10003 /* Config.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10003 /* Config.swift */; };
 		A10004 /* APIClient.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10004 /* APIClient.swift */; };
 		A10005 /* AuthManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10005 /* AuthManager.swift */; };
+		A10050 /* AppearanceManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10050 /* AppearanceManager.swift */; };
 		A10006 /* LoginView.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10006 /* LoginView.swift */; };
 		A10007 /* HomeView.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10007 /* HomeView.swift */; };
 		A10008 /* HomeViewModel.swift in Sources */ = {isa = PBXBuildFile; fileRef = B10008 /* HomeViewModel.swift */; };
@@ -57,6 +58,7 @@
 		B10003 /* Config.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Config.swift; sourceTree = "<group>"; };
 		B10004 /* APIClient.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = APIClient.swift; sourceTree = "<group>"; };
 		B10005 /* AuthManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AuthManager.swift; sourceTree = "<group>"; };
+		B10050 /* AppearanceManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppearanceManager.swift; sourceTree = "<group>"; };
 		B10006 /* LoginView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LoginView.swift; sourceTree = "<group>"; };
 		B10007 /* HomeView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HomeView.swift; sourceTree = "<group>"; };
 		B10008 /* HomeViewModel.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HomeViewModel.swift; sourceTree = "<group>"; };
@@ -137,6 +139,7 @@
 			children = (
 				B10004 /* APIClient.swift */,
 				B10005 /* AuthManager.swift */,
+				B10050 /* AppearanceManager.swift */,
 			);
 			path = Core;
 			sourceTree = "<group>";
@@ -411,6 +414,7 @@
 				A10003 /* Config.swift in Sources */,
 				A10004 /* APIClient.swift in Sources */,
 				A10005 /* AuthManager.swift in Sources */,
+				A10050 /* AppearanceManager.swift in Sources */,
 				A10006 /* LoginView.swift in Sources */,
 				A10007 /* HomeView.swift in Sources */,
 				A10008 /* HomeViewModel.swift in Sources */,

ios/Platform/Platform/Core/AppearanceManager.swift

@@ -0,0 +1,43 @@
+import SwiftUI
+
+@Observable
+final class AppearanceManager {
+    enum Mode: String, CaseIterable {
+        case system, light, dark
+
+        var label: String {
+            switch self {
+            case .system: return "System"
+            case .light: return "Light"
+            case .dark: return "Dark"
+            }
+        }
+
+        var icon: String {
+            switch self {
+            case .system: return "circle.lefthalf.filled"
+            case .light: return "sun.max.fill"
+            case .dark: return "moon.fill"
+            }
+        }
+
+        var colorScheme: ColorScheme? {
+            switch self {
+            case .system: return nil
+            case .light: return .light
+            case .dark: return .dark
+            }
+        }
+    }
+
+    var mode: Mode {
+        didSet {
+            UserDefaults.standard.set(mode.rawValue, forKey: "appearance_mode")
+        }
+    }
+
+    init() {
+        let saved = UserDefaults.standard.string(forKey: "appearance_mode") ?? "system"
+        mode = Mode(rawValue: saved) ?? .system
+    }
+}

ios/Platform/Platform/Features/Home/HomeView.swift

@@ -3,6 +3,7 @@ import PhotosUI
 
 struct HomeView: View {
     @Environment(AuthManager.self) private var auth
+    @Environment(AppearanceManager.self) private var appearance
     @State private var vm = HomeViewModel()
     @State private var ringAnimated = false
     @Binding var selectedTab: Int
@@ -50,6 +51,18 @@ struct HomeView: View {
                                 }
                             }
                             Divider()
+                            Menu {
+                                ForEach(AppearanceManager.Mode.allCases, id: \.self) { mode in
+                                    Button {
+                                        appearance.mode = mode
+                                    } label: {
+                                        Label(mode.label, systemImage: mode.icon)
+                                    }
+                                }
+                            } label: {
+                                Label("Appearance", systemImage: appearance.mode.icon)
+                            }
+                            Divider()
                             Button(role: .destructive) {
                                 Task { await auth.logout() }
                             } label: {

ios/Platform/Platform/PlatformApp.swift

@@ -3,11 +3,14 @@ import SwiftUI
 @main
 struct PlatformApp: App {
     @State private var authManager = AuthManager()
+    @State private var appearance = AppearanceManager()
 
     var body: some Scene {
         WindowGroup {
             ContentView()
                 .environment(authManager)
+                .environment(appearance)
+                .preferredColorScheme(appearance.mode.colorScheme)
         }
     }
 }