feat: add GroupFilterViewModel and GroupFilterView sidebar

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WYqycDFsynHH9VnnK7LNSf

MyPass/ViewModels/GroupFilterViewModel.swift

@@ -0,0 +1,27 @@
+import Foundation
+import Combine
+import MyPassCore
+
+@MainActor
+final class GroupFilterViewModel: ObservableObject {
+    @Published var selectedGroupIds: Set<UUID> = []
+
+    private let session: VaultSession
+
+    init(session: VaultSession) {
+        self.session = session
+    }
+
+    func isSelected(_ group: MyPassCore.Group) -> Bool {
+        selectedGroupIds.contains(group.id)
+    }
+
+    func toggle(_ group: MyPassCore.Group) {
+        guard let root = session.database?.root else { return }
+        selectedGroupIds = GroupSelection.toggling(group.id, in: root, current: selectedGroupIds)
+    }
+
+    func clear() {
+        selectedGroupIds = []
+    }
+}

MyPass/Views/GroupFilterView.swift

@@ -0,0 +1,49 @@
+import SwiftUI
+import MyPassCore
+
+struct GroupFilterView: View {
+    @ObservedObject var vm: GroupFilterViewModel
+    let rootGroup: MyPassCore.Group
+
+    var body: some View {
+        List {
+            if !vm.selectedGroupIds.isEmpty {
+                Button("Clear Filter", action: vm.clear)
+            }
+            GroupFilterNode(group: rootGroup, vm: vm)
+        }
+        .navigationTitle("Groups")
+    }
+}
+
+private struct GroupFilterNode: View {
+    let group: MyPassCore.Group
+    @ObservedObject var vm: GroupFilterViewModel
+
+    var body: some View {
+        if group.subgroups.isEmpty {
+            row
+        } else {
+            DisclosureGroup {
+                ForEach(group.subgroups) { sub in
+                    GroupFilterNode(group: sub, vm: vm)
+                }
+            } label: {
+                row
+            }
+        }
+    }
+
+    private var row: some View {
+        Button {
+            vm.toggle(group)
+        } label: {
+            HStack {
+                Image(systemName: vm.isSelected(group) ? "checkmark.circle.fill" : "circle")
+                    .foregroundStyle(vm.isSelected(group) ? Color.accentColor : Color.secondary)
+                Label(group.name, systemImage: "folder")
+            }
+        }
+        .buttonStyle(.plain)
+    }
+}