refactor(frontend): colocate admin components and split service layer

Move route-specific admin components from components/common/admin into
app/(main)/admin/<feature>/components/. Split AdminService god object into
domain services, fix UploadService to use BaseService, add AdminUploadService,
consolidate DB export into DbManageService, and migrate consumers to the
unified services entry.

frontend/components/common/settings/auth-source-modal.tsx

@@ -7,7 +7,7 @@ import {Dialog, DialogContent, DialogDescription, DialogHeader, DialogTitle} fro
 import {Input} from "@/components/ui/input"
 import {Label} from "@/components/ui/label"
 import {Switch} from "@/components/ui/switch"
-import {AdminService} from "@/lib/services/admin"
+import services from "@/lib/services"
 import type {AuthSource, AuthSourceRequest} from "@/lib/services/admin"
 
 const emptyForm: AuthSourceRequest = {
@@ -63,9 +63,9 @@ export function AuthSourceModal({
     setSaving(true)
     try {
       if (source) {
-        await AdminService.updateAuthSource(source.id, form)
+        await services.adminAuthSource.updateAuthSource(source.id, form)
       } else {
-        await AdminService.createAuthSource(form)
+        await services.adminAuthSource.createAuthSource(form)
       }
       await onChanged()
       toast.success("认证源已保存")