perf(ui): show list settings modal before its seven-round-trip load finishes

OpenListSettingsAsync/CreateListAsync used to await LoadAsync (name/agent
config/list_config x2/ticket settings/ticket projects, all serial) before
showing the window -- an unreachable ticket system alone could add a 10s
HTTP timeout to every open. LoadAsync now runs via BeginLoad (fire-and-forget,
mirrors UsageMonitorModalViewModel), the modal shows immediately and fields
fill in behind it.

GetListConfigAsync no longer runs twice per open -- AgentConfigEditorViewModel
exposes the row it already fetched (LastLoadedListConfig) instead of the
caller re-fetching it. Ticket-project loading is split into its own
fire-and-forget step so a slow/unreachable ticket system can't block the
rest of the fields, and its tri-state Save logic now also treats "never
finished loading" like "not available" -- leaving the stored
TicketProjectId link untouched instead of overwriting it with 0. Save/Delete
are gated (CanExecute) on the core load being done, so a save can't land
before the fields it writes are populated.

Not measured with OperationTiming against a live worker in this session (no
running app instance available) -- verified instead via 4 new unit tests
that assert GetListConfigAsync fires exactly once and that a hung/failing
ticket-projects call neither blocks LoadAsync's other fields nor corrupts
the saved TicketProjectId. Before/after OperationTiming numbers and a visual
pass are still open follow-ups.

src/ClaudeDo.Ui/ViewModels/Agent/AgentConfigEditorViewModel.cs

@@ -236,6 +236,10 @@ public sealed partial class AgentConfigEditorViewModel : ViewModelBase, IDisposa
         return names.Count == 0 ? null : names;
     }
 
+    // The list_config row fetched by the most recent LoadForListAsync — exposed so a caller that
+    // needs the same row (ListSettingsModalViewModel) can reuse it instead of fetching it again.
+    public ListConfigDto? LastLoadedListConfig { get; private set; }
+
     public async System.Threading.Tasks.Task LoadForListAsync(string listId, CancellationToken ct = default)
     {
         _suppressSave = true;
@@ -246,6 +250,7 @@ public sealed partial class AgentConfigEditorViewModel : ViewModelBase, IDisposa
             await LoadGlobalDefaultsAsync();
 
             var cfg = await _worker.GetListConfigAsync(listId);
+            LastLoadedListConfig = cfg;
             ApplyConfig(cfg?.Model, cfg?.MaxTurns, cfg?.SystemPrompt, cfg?.AgentPath, cfg?.PermissionMode);
             await ReloadSessionSkillsAsync(cfg?.SessionSkills);