Raise deployment target to iOS 18 and modernize SwiftUI APIs

Adopt modern SwiftUI patterns now that the minimum target is iOS 18:
NavigationStack, .toolbar, .tint, new Tab API with sidebarAdaptable
style, and remove iOS 17 availability checks. Add Liquid Glass effect
support for iOS 26 in TimerView and fix an optional interpolation
warning in AppState.

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

Nextcloud Cookbook iOS Client/Views/MainView.swift

@@ -10,46 +10,40 @@ import SwiftUI
 struct MainView: View {
     @StateObject var appState = AppState()
     @StateObject var groceryList = GroceryList()
-    
+
     // Tab ViewModels
     @StateObject var recipeViewModel = RecipeTabView.ViewModel()
     @StateObject var searchViewModel = SearchTabView.ViewModel()
-    
+
+    @State private var selectedTab: Tab = .recipes
+
     enum Tab {
         case recipes, search, groceryList
     }
-    
+
     var body: some View {
-        TabView {
-            RecipeTabView()
-                .environmentObject(recipeViewModel)
-                .environmentObject(appState)
-                .environmentObject(groceryList)
-                .tabItem {
-                    Label("Recipes", systemImage: "book.closed.fill")
-                }
-                .tag(Tab.recipes)
-            
-            SearchTabView()
-                .environmentObject(searchViewModel)
-                .environmentObject(appState)
-                .environmentObject(groceryList)
-                .tabItem {
-                    Label("Search", systemImage: "magnifyingglass")
-                }
-                .tag(Tab.search)
-            
-            GroceryListTabView()
-                .environmentObject(groceryList)
-                .tabItem {
-                    if #available(iOS 17.0, *) {
-                        Label("Grocery List", systemImage: "storefront")
-                    } else {
-                        Label("Grocery List", systemImage: "heart.text.square")
-                    }
-                }
-                .tag(Tab.groceryList)
+        TabView(selection: $selectedTab) {
+            SwiftUI.Tab("Recipes", systemImage: "book.closed.fill", value: .recipes) {
+                RecipeTabView()
+                    .environmentObject(recipeViewModel)
+                    .environmentObject(appState)
+                    .environmentObject(groceryList)
+            }
+
+            SwiftUI.Tab("Search", systemImage: "magnifyingglass", value: .search, role: .search) {
+                SearchTabView()
+                    .environmentObject(searchViewModel)
+                    .environmentObject(appState)
+                    .environmentObject(groceryList)
+            }
+
+            SwiftUI.Tab("Grocery List", systemImage: "storefront", value: .groceryList) {
+                GroceryListTabView()
+                    .environmentObject(groceryList)
+            }
         }
+        .tabViewStyle(.sidebarAdaptable)
+        .modifier(TabBarMinimizeModifier())
         .task {
             recipeViewModel.presentLoadingIndicator = true
             await appState.getCategories()