Add authentication and session management improvements

Introduce navigation guards for authentication and admin access within routes. Replace localStorage usage with secure token storage via httpOnly cookies, and add token blacklisting upon logout. Enhance token refresh mechanism and session expiration handling to improve security and user experience.

frontend/src/components/TheNavbar.vue

@@ -6,7 +6,8 @@
         <span class="navbar-toggler-icon"></span>
       </button>
       <div class="collapse navbar-collapse" id="navbarSupportedContent">
-        <ul class="navbar-nav me-auto mb-2 mb-lg-0">
+        <!-- Show these links only when user is authenticated -->
+        <ul class="navbar-nav me-auto mb-2 mb-lg-0" v-if="isAuthenticated">
           <li class="nav-item">
             <router-link :to="{name: 'browse'}" class="nav-link" >Browse</router-link>
           </li>
@@ -26,6 +27,12 @@
             <a class="nav-link" @click="logout">Log Out</a>
           </li>
         </ul>
+        <!-- Show login link when user is not authenticated -->
+        <ul class="navbar-nav me-auto mb-2 mb-lg-0" v-else>
+          <li class="nav-item">
+            <router-link :to="{name: 'login'}" class="nav-link">Log In</router-link>
+          </li>
+        </ul>
       </div>
     </div>
   </nav>
@@ -42,6 +49,11 @@ export default {
       visible: false
     }
   },
+  computed: {
+    isAuthenticated() {
+      return !!this.$store.state.jwt;
+    }
+  },
   methods: {
     logout () {
       store.commit('logOut')