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/Modules/Settings/WorkspacesTab.qml

@@ -155,6 +155,16 @@ Item {
                     onToggled: checked => SettingsData.set("reverseScrolling", checked)
                 }
 
+                SettingsToggleRow {
+                    settingKey: "workspaceDragReorder"
+                    tags: ["workspace", "drag", "reorder", "sort", "move"]
+                    text: I18n.tr("Drag to Reorder")
+                    description: I18n.tr("Drag workspace indicators to reorder them")
+                    checked: SettingsData.workspaceDragReorder
+                    visible: CompositorService.isNiri
+                    onToggled: checked => SettingsData.set("workspaceDragReorder", checked)
+                }
+
                 SettingsToggleRow {
                     settingKey: "dwlShowAllTags"
                     tags: ["dwl", "tags", "workspace"]