feat: add iOS support and harden receipt scanning

app/ios/ScanReceipts/App/MainTabView.swift

@@ -0,0 +1,30 @@
+import SwiftUI
+
+/// Shown once `AppState.phase == .signedIn`. Each tab's root view is built
+/// independently (see the Features/ subfolders) and referenced here only by
+/// its type name — this file is the one integration point between them, so
+/// none of the three needs to know the other two exist.
+struct MainTabView: View {
+    var body: some View {
+        TabView {
+            // Features/Scan/ScanTabView.swift
+            ScanTabView()
+                .tabItem { Label("Scannen", systemImage: "camera.viewfinder") }
+
+            // Features/Receipts/ReceiptsListView.swift
+            ReceiptsListView()
+                .tabItem { Label("Belege", systemImage: "list.bullet.rectangle") }
+
+            // Features/Settings/SettingsView.swift
+            SettingsView()
+                .tabItem { Label("Konto", systemImage: "person.crop.circle") }
+        }
+        .tint(.zenithBlack)
+        // Solid white tab bar, no translucent system blur — the design
+        // system rejects soft/blurred depth cues in favor of flat surfaces
+        // with a hard 1px edge (the hairline the system automatically draws
+        // at the top of an opaque tab bar stands in for that border here).
+        .toolbarBackground(Color.zenithSurface, for: .tabBar)
+        .toolbarBackground(.visible, for: .tabBar)
+    }
+}