Add centralized API client with axios interceptors, remove vue-axios

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/views/MainContainer.vue

@@ -85,11 +85,6 @@ export default {
       'refreshToken',
     ],),
   },
-  created() {
-    // Save token in Headers.
-    const token = getCookie('luciaToken');
-    this.$http.defaults.headers.common['Authorization'] = `Bearer ${token}`;
-  },
   // 重新整理畫面以及第一次進入網頁時，beforeRouteEnter這個hook會被執行，然而beforeRouteUpdate不會被執行
     // PSEUDOCODE
     // if (not logged in) {