feat(settings): add Mouse & Touchpad settings tab for Niri (#2905)

* feat(settings): add Mouse & Trackpad settings tab

* style(settings): clarify touchpad natural scroll description

* chore(settings): update settings search index

* refactor(settings): unify Mouse & Trackpad terminology to Mouse & Touchpad

* feat(setup): deploy default dms/input.kdl on setup

* style(niri): restore include section comment in base config template

* refactor(niri): remove redundant input block from base config template

* refactor(niri): restore keyboard and non-mouse input config to base template

* feat(settings): add touchpad disable-on-external-mouse toggle

* feat(settings): add left-handed, scroll-factor and dwt options

* feat(settings): add middle-emulation, scroll-method, tap-and-drag and drag-lock options

* refactor(settings): re-order mouse and touchpad UI options logically

quickshell/Modals/Settings/SettingsContent.qml

@@ -718,5 +718,20 @@ FocusScope {
                     Qt.callLater(() => item.forceActiveFocus());
             }
         }
+
+        Loader {
+            id: mouseTouchpadLoader
+            anchors.fill: parent
+            active: root.currentIndex === 44
+            visible: active
+            focus: active
+
+            sourceComponent: MouseTouchpadTab {}
+
+            onActiveChanged: {
+                if (active && item)
+                    Qt.callLater(() => item.forceActiveFocus());
+            }
+        }
     }
 }

quickshell/Modals/Settings/SettingsSidebar.qml

@@ -319,6 +319,13 @@ Rectangle {
                     "icon": "headphones",
                     "tabIndex": 29
                 },
+                {
+                    "id": "mouse_touchpad",
+                    "text": I18n.tr("Mouse & Touchpad"),
+                    "icon": "mouse",
+                    "tabIndex": 44,
+                    "niriOnly": true
+                },
                 {
                     "id": "locale",
                     "text": I18n.tr("Locale"),