fix: correct add-entry default group and clear search on hide

- GroupFilterViewModel now tracks lastToggledGroupId (the single group
  most recently toggled to a non-empty selection), since toggling a
  group with subgroups expands selectedGroupIds to include the whole
  subtree, breaking the previous count==1 check used to infer the
  active filter group.
- VaultViewModel exposes lastToggledGroupId, forwarded from
  GroupFilterViewModel by VaultRootView (ContentView.swift), and
  EntryListView.defaultGroupId now reads it instead of the broken
  selectedGroupIds.count == 1 check, so the add-entry sheet defaults
  new entries into the group actually being filtered by, not silently
  back to root.
- EntryListView's search toggle button now clears vm.searchQuery when
  hiding the search bar, so a hidden bar can no longer keep filtering
  the list invisibly.

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

MyPass/ContentView.swift

@@ -74,5 +74,8 @@ private struct VaultRootView: View {
         .onChange(of: filterVM.selectedGroupIds) { _, newValue in
             vaultVM.selectedGroupIds = newValue
         }
+        .onChange(of: filterVM.lastToggledGroupId) { _, newValue in
+            vaultVM.lastToggledGroupId = newValue
+        }
     }
 }