refactor(frontend): 完成所有组件的内联SVG统一替换为Icon组件

- 扩展 Icon.vue 组件，新增 60+ 图标路径
  - 导航类: arrowRight, arrowLeft, arrowUp, arrowDown, chevronUp, externalLink
  - 状态类: checkCircle, xCircle, exclamationCircle, exclamationTriangle, infoCircle
  - 用户类: user, userCircle, userPlus, users
  - 文档类: document, clipboard, copy, inbox
  - 操作类: download, upload, filter, sort
  - 安全类: key, lock, shield
  - UI类: menu, calendar, home, terminal, gift, creditCard, mail
  - 数据类: chartBar, trendingUp, database, cube
  - 其他: bolt, sparkles, cloud, server, sun, moon, book 等

- 重构 56 个 Vue 组件，用 Icon 组件替换内联 SVG
  - 净减少约 2200 行代码
  - 提升代码可维护性和一致性
  - 统一图标样式和尺寸管理

frontend/src/components/layout/AppHeader.vue

@@ -8,19 +8,7 @@
           class="btn-ghost btn-icon lg:hidden"
           aria-label="Toggle Menu"
         >
-          <svg
-            class="h-5 w-5"
-            fill="none"
-            viewBox="0 0 24 24"
-            stroke="currentColor"
-            stroke-width="1.5"
-          >
-            <path
-              stroke-linecap="round"
-              stroke-linejoin="round"
-              d="M3.75 6.75h16.5M3.75 12h16.5m-16.5 5.25h16.5"
-            />
-          </svg>
+          <Icon name="menu" size="md" />
         </button>
 
         <div class="hidden lg:block">
@@ -84,19 +72,7 @@
                 {{ user.role }}
               </div>
             </div>
-            <svg
-              class="hidden h-4 w-4 text-gray-400 md:block"
-              fill="none"
-              viewBox="0 0 24 24"
-              stroke="currentColor"
-              stroke-width="1.5"
-            >
-              <path
-                stroke-linecap="round"
-                stroke-linejoin="round"
-                d="M19.5 8.25l-7.5 7.5-7.5-7.5"
-              />
-            </svg>
+            <Icon name="chevronDown" size="sm" class="hidden text-gray-400 md:block" />
           </button>
 
           <!-- Dropdown Menu -->
@@ -122,36 +98,12 @@
 
               <div class="py-1">
                 <router-link to="/profile" @click="closeDropdown" class="dropdown-item">
-                  <svg
-                    class="h-4 w-4"
-                    fill="none"
-                    viewBox="0 0 24 24"
-                    stroke="currentColor"
-                    stroke-width="1.5"
-                  >
-                    <path
-                      stroke-linecap="round"
-                      stroke-linejoin="round"
-                      d="M15.75 6a3.75 3.75 0 11-7.5 0 3.75 3.75 0 017.5 0zM4.501 20.118a7.5 7.5 0 0114.998 0A17.933 17.933 0 0112 21.75c-2.676 0-5.216-.584-7.499-1.632z"
-                    />
-                  </svg>
+                  <Icon name="user" size="sm" />
                   {{ t('nav.profile') }}
                 </router-link>
 
                 <router-link to="/keys" @click="closeDropdown" class="dropdown-item">
-                  <svg
-                    class="h-4 w-4"
-                    fill="none"
-                    viewBox="0 0 24 24"
-                    stroke="currentColor"
-                    stroke-width="1.5"
-                  >
-                    <path
-                      stroke-linecap="round"
-                      stroke-linejoin="round"
-                      d="M15.75 5.25a3 3 0 013 3m3 0a6 6 0 01-7.029 5.912c-.563-.097-1.159.026-1.563.43L10.5 17.25H8.25v2.25H6v2.25H2.25v-2.818c0-.597.237-1.17.659-1.591l6.499-6.499c.404-.404.527-1 .43-1.563A6 6 0 1121.75 8.25z"
-                    />
-                  </svg>
+                  <Icon name="key" size="sm" />
                   {{ t('nav.apiKeys') }}
                 </router-link>
 
@@ -246,6 +198,7 @@ import { useI18n } from 'vue-i18n'
 import { useAppStore, useAuthStore, useOnboardingStore } from '@/stores'
 import LocaleSwitcher from '@/components/common/LocaleSwitcher.vue'
 import SubscriptionProgressMini from '@/components/common/SubscriptionProgressMini.vue'
+import Icon from '@/components/icons/Icon.vue'
 
 const router = useRouter()
 const route = useRoute()