feat(niri): Add drag-and-drop workspace reordering (#1569)

* feat(niri): Add drag-and-drop workspace reordering

Add interactive drag-and-drop reordering for Niri workspace indicators
with smooth animations matching the system tray behavior.

- Add moveWorkspaceToIndex() to NiriService for workspace reordering
- Implement drag detection with 5px threshold
- Add shift animation for items between source and target
- Clamp drag offset to stay within workspace row bounds
- Reset drag state when workspace list changes during drag
- Visual feedback: opacity change, border highlight on drag/drop target

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat(settings): Add workspace drag reorder toggle

Add workspaceDragReorder setting to enable/disable workspace
drag-and-drop reordering. Enabled by default, only visible on Niri.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

quickshell/Common/SettingsData.qml

@@ -241,6 +241,7 @@ Singleton {
     property bool showWorkspacePadding: false
     property bool workspaceScrolling: false
     property bool showWorkspaceApps: false
+    property bool workspaceDragReorder: true
     property bool groupWorkspaceApps: true
     property int maxWorkspaceIcons: 3
     property int workspaceAppIconSizeOffset: 0