chore(core): set read-only mode on mobile device (#7651)

Close [BS-795](https://linear.app/affine-design/issue/BS-795/affine-mobile-设置只读模式)

- Set read-only mode on mobile device
- Add mobile only support read-only warning toast
- remove `user-select: none` so that user can select text in read-only mode

packages/frontend/i18n/src/resources/en.json

@@ -1325,6 +1325,7 @@
   "com.affine.toastMessage.successfullyDeleted": "Successfully deleted",
   "com.affine.today": "Today",
   "com.affine.tomorrow": "Tomorrow",
+  "com.affine.top-tip.mobile": "Limited to view-only on mobile.",
   "com.affine.trashOperation.delete": "Delete",
   "com.affine.trashOperation.delete.description": "Once deleted, you can't undo this action. Do you confirm?",
   "com.affine.trashOperation.delete.title": "Permanently delete",