refactor: 重构 API 层目录结构 & 样式模块化拆分

- API 层按业务域拆分（api/auth/, api/file/, api/system/*）
- 类型定义从 types/api/ 移入对应 api 模块内（就近原则）
- 公共类型统一为 api/common.ts，移除冗余类型重导出
- 样式文件按职责拆分（base/, layout/, vendors/），移除 common.scss
- 移除失效的单元测试文件

src/views/dashboard/index.vue

@@ -1,9 +1,9 @@
 <template>
-  <div class="relative p-6">
+  <div class="relative p-5">
     <!-- github 角标 -->
     <github-corner class="absolute top-0 right-0 z-1 border-0" />
 
-    <el-card shadow="never" class="mt-2">
+    <el-card shadow="never">
       <div class="flex flex-wrap">
         <!-- 左侧问候语区域 -->
         <div class="flex-1 flex items-start">
@@ -383,7 +383,7 @@ import { dayjs } from "element-plus";
 import { ref } from "vue";
 import { useRouter } from "vue-router";
 import LogAPI from "@/api/system/log";
-import type { VisitStatsDetail, VisitTrendDetail } from "@/types/api";
+import type { VisitStatsDetail, VisitTrendDetail } from "@/api/system/log";
 import { useUserStore } from "@/store/modules/user";
 import { formatGrowthRate } from "@/utils";
 import { useTransition, useDateFormat } from "@vueuse/core";