refactor: extract various constants

frontend/src/ui/useFloatingMenu.ts

@@ -1,8 +1,7 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
 import type { MutableRefObject, CSSProperties } from 'react';
 import { clamp } from '../utils/math';
-
-const DEFAULT_VIEWPORT_MARGIN = 8;
+import { DEFAULT_VIEWPORT_MARGIN } from '../constants/ui';
 
 type PositionStrategy = 'fixed' | 'absolute' | (string & {});