fix(account): Anmelden-Button + ManaAuthGate-Wiring

AccountView hatte zwar einen Status-Text aber keinen Login-Button,
und der ManaAuthGate war überhaupt nicht im App-Tree eingebaut —
Guest-Mode-User konnten sich nirgends anmelden.

- ZitareNativeApp: ManaAuthGate(auth:) instantiiert + via environment
  durchgereicht
- RootView: .manaBrand(ZitareBrand.manaBrand) +
  .manaAuthGate(authGate) { ManaLoginView(…) } für globales
  Sign-In-Sheet
- AccountView: authActionCard mit "Mit mana-Konto anmelden" /
  "Abmelden" (keepGuestMode: true)
- ZitareBrand neu (paper-Theme-Brücke zu ManaBrandConfig)
- project.yml: platformFilter: iOS für Widget+Share-Extensions
  (macOS-Build war pre-existing kaputt mit "embedded iOS content")

iOS + macOS BUILD SUCCEEDED.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Sources/App/RootView.swift

@@ -1,3 +1,4 @@
+import ManaAuthUI
 import ManaCore
 import ManaWebShell
 import SwiftUI
@@ -43,6 +44,7 @@ private func makeWebShellConfig() -> WebShellConfig {
 /// die App und routen in den passenden Tab.
 struct RootView: View {
     @Environment(AuthClient.self) private var auth
+    @Environment(ManaAuthGate.self) private var authGate
     @State private var selectedTab: AppTab = .read
     @State private var readTarget = WebTarget(url: AppConfig.webBaseURL)
     @State private var exploreTarget = WebTarget(
@@ -76,6 +78,17 @@ struct RootView: View {
             .toolbarBackground(ZitareTheme.background, for: .windowToolbar)
             .toolbarBackground(.visible, for: .windowToolbar)
         #endif
+        .manaBrand(ZitareBrand.manaBrand)
+        .manaAuthGate(authGate) {
+            NavigationStack {
+                ManaLoginView(
+                    auth: auth,
+                    onSignUpTapped: {},
+                    onForgotTapped: {}
+                )
+                .manaBrand(ZitareBrand.manaBrand)
+            }
+        }
         .task {
             await probeHealth()
         }

Sources/App/ZitareNativeApp.swift

@@ -1,3 +1,4 @@
+import ManaAuthUI
 import ManaCore
 import SwiftData
 import SwiftUI
@@ -6,12 +7,14 @@ import WidgetKit
 @main
 struct ZitareNativeApp: App {
     @State private var auth: AuthClient
+    @State private var authGate: ManaAuthGate
     private let snapshotContainer: ModelContainer?
 
     init() {
         let auth = AuthClient(config: AppConfig.manaAppConfig)
         auth.bootstrap()
         _auth = State(initialValue: auth)
+        _authGate = State(initialValue: ManaAuthGate(auth: auth))
         do {
             snapshotContainer = try SnapshotContainer.make()
         } catch {
@@ -29,6 +32,7 @@ struct ZitareNativeApp: App {
         WindowGroup {
             RootView()
                 .environment(auth)
+                .environment(authGate)
                 .tint(ZitareTheme.primary)
                 .task {
                     await refreshSnapshot()