fix: update window title when the active workspace is renamed

[JC-Chung]

Summary

When a workspace is renamed via the "Configure Workspace" dialog, the main window title (shown in the taskbar) keeps displaying the old name until the next ActivePage/ActiveWorkspace change triggers PostActivePageChanged().

Root Cause

Launcher.Title is a snapshot string built in PostActivePageChanged(). Nothing subscribes to Workspace.Name changes, so renaming the active workspace never rebuilds the title.

Changes

• src/ViewModels/Launcher.cs
  • Subscribe to Workspace.PropertyChanged in the ActiveWorkspace setter (unsubscribing the previous workspace to avoid stale handlers).
  • Add OnActiveWorkspacePropertyChanged, which calls PostActivePageChanged() when Name changes on the active workspace.

The existing _ignoreIndexChange guard inside PostActivePageChanged() prevents redundant rebuilds during SwitchWorkspace().

Test

1. Create two workspaces so the workspace name appears in the window title.
2. Open "Configure Workspace" and rename the active workspace.
3. The window title now updates immediately; previously it stayed stale until switching tabs or workspaces.

[love-linger]

I've pushed my fixed for this BUG.