fix: use sheet-presented group filter on iOS instead of NavigationSplitView

Confirmed by hands-on testing: NavigationSplitView's compact-width
collapse only pushes into the detail column when the sidebar drives
navigation via row selection. GroupFilterView is a multi-select filter,
not a picker, so on iPhone it showed only the sidebar with no way to
reach the entry list at all -- exactly the risk the final whole-branch
review flagged as unverified.

iOS now uses a plain NavigationStack with EntryListView as the root and
GroupFilterView presented as a sheet via the hamburger button. macOS
keeps the persistent NavigationSplitView sidebar, which does work
correctly at regular width.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WYqycDFsynHH9VnnK7LNSf

MyPass/ContentView.swift

@@ -45,7 +45,11 @@ struct ContentView: View {
 private struct VaultRootView: View {
     @StateObject private var vaultVM: VaultViewModel
     @StateObject private var filterVM: GroupFilterViewModel
+    #if os(macOS)
     @State private var columnVisibility: NavigationSplitViewVisibility = .all
+    #else
+    @State private var showFilterSheet = false
+    #endif
 
     init(session: VaultSession) {
         _vaultVM = StateObject(wrappedValue: VaultViewModel(session: session))
@@ -53,6 +57,19 @@ private struct VaultRootView: View {
     }
 
     var body: some View {
+        content
+            .onChange(of: filterVM.selectedGroupIds) { _, newValue in
+                vaultVM.selectedGroupIds = newValue
+            }
+            .onChange(of: filterVM.lastToggledGroupId) { _, newValue in
+                vaultVM.lastToggledGroupId = newValue
+            }
+    }
+
+    #if os(macOS)
+    // macOS has room for a persistent sidebar; NavigationSplitView's columnVisibility
+    // toggle works correctly at regular width.
+    private var content: some View {
         NavigationSplitView(columnVisibility: $columnVisibility) {
             if let root = vaultVM.session.database?.root {
                 GroupFilterView(vm: filterVM, rootGroup: root)
@@ -71,11 +88,38 @@ private struct VaultRootView: View {
                     }
             }
         }
-        .onChange(of: filterVM.selectedGroupIds) { _, newValue in
-            vaultVM.selectedGroupIds = newValue
+    }
+    #else
+    // NavigationSplitView's compact-width collapse only pushes to detail when the
+    // sidebar drives navigation via row selection. Our sidebar is a multi-select
+    // filter, not a picker, so on iPhone it would just show the sidebar forever with
+    // no way to reach the entry list. Use a plain stack with the entry list as the
+    // root, and present the group filter as a sheet instead.
+    private var content: some View {
+        NavigationStack {
+            EntryListView(vm: vaultVM)
+                .toolbar {
+                    ToolbarItem(placement: .navigation) {
+                        Button {
+                            showFilterSheet = true
+                        } label: {
+                            Image(systemName: "line.3.horizontal")
+                        }
+                    }
+                }
         }
-        .onChange(of: filterVM.lastToggledGroupId) { _, newValue in
-            vaultVM.lastToggledGroupId = newValue
+        .sheet(isPresented: $showFilterSheet) {
+            NavigationStack {
+                if let root = vaultVM.session.database?.root {
+                    GroupFilterView(vm: filterVM, rootGroup: root)
+                        .toolbar {
+                            ToolbarItem(placement: .confirmationAction) {
+                                Button("Done") { showFilterSheet = false }
+                            }
+                        }
+                }
+            }
         }
     }
+    #endif
 }