fix: 移除所有硬编码的localhost:8080，使用相对路径

- 创建utils/config.ts集中管理API_BASE和文件URL
- 删除.env文件（VITE_SERVER_API_URL=http://localhost:8080）
- env.ts默认API前缀改为/api/v1匹配后端路由
- 替换16处硬编码的localhost:8080引用

frontend/src/components/app-sidebar/team-switcher.vue

@@ -3,6 +3,8 @@ import { ref } from 'vue'
 
 import type { Team } from './types'
 
+import { getFileUrl } from '@/utils/config'
+
 const { teams } = defineProps<{
   teams: Team[]
 }>()
@@ -10,11 +12,7 @@ const { teams } = defineProps<{
 const activeTeam = ref<Team>(teams[0])
 
 function getAssetUrl(path: string) {
-  if (!path)
-    return ''
-  if (path.startsWith('http'))
-    return path
-  return `${import.meta.env.VITE_API_BASE || 'http://localhost:8080'}${path}`
+  return getFileUrl(path)
 }
 </script>