feat(frontend): redesign tab bar icons in wuxing sandbox style

- Replace all 5 tab bar icons with element-symbol shapes matching
  the energy sandbox (wuxing-sandbox) visual language:
  行(wood/leaf) 身(earth/mountain) 智(metal/diamond) 心(fire/flame) 富(water/drop)
- Use dimension colors from the sandbox palette for active state,
  gray for inactive state
- Remove old tab-home icons (replaced by tab-action)
- Update pages.json to reference new tab-action filenames

cfc-frontend/pages.json

@@ -1315,8 +1315,8 @@
       {
         "pagePath": "pages/index/index",
         "text": "行",
-        "iconPath": "static/tab-home.png",
-        "selectedIconPath": "static/tab-home-active.png"
+        "iconPath": "static/tab-action.png",
+        "selectedIconPath": "static/tab-action-active.png"
       },
       {
         "pagePath": "pages/mind/index",