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/Services/NiriService.qml

@@ -1452,6 +1452,19 @@ Singleton {
         });
     }
 
+    function moveWorkspaceToIndex(workspaceIdx, targetIndex) {
+        return send({
+            "Action": {
+                "MoveWorkspaceToIndex": {
+                    "index": targetIndex,
+                    "reference": {
+                        "Index": workspaceIdx
+                    }
+                }
+            }
+        });
+    }
+
     IpcHandler {
         function screenshot(): string {
             if (!CompositorService.isNiri) {