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/app/(main)/admin/users/components/create-user-modal.tsx

@@ -0,0 +1,182 @@
+"use client"
+
+import {useEffect, useState} from "react"
+import {Button} from "@/components/ui/button"
+import {Dialog, DialogContent, DialogDescription, DialogHeader, DialogTitle} from "@/components/ui/dialog"
+import {Input} from "@/components/ui/input"
+import {Label} from "@/components/ui/label"
+import {Switch} from "@/components/ui/switch"
+import {useAdminUsers} from "@/contexts/admin-users-context"
+import type {CreateUserRequest} from "@/lib/services/admin"
+
+const emptyForm: CreateUserRequest = {
+  username: "",
+  password: "",
+  nickname: "",
+  email: "",
+  is_active: true,
+  is_admin: false,
+}
+
+export function CreateUserModal({
+  isOpen,
+  onClose,
+}: {
+  isOpen: boolean
+  onClose: () => void
+}) {
+  const { createUser } = useAdminUsers()
+  const [form, setForm] = useState<CreateUserRequest>(emptyForm)
+  const [saving, setSaving] = useState(false)
+  const [errors, setErrors] = useState<Record<string, string>>({})
+
+  useEffect(() => {
+    if (isOpen) {
+      setForm(emptyForm)
+      setErrors({})
+    } else {
+      setSaving(false)
+    }
+  }, [isOpen])
+
+  const validate = () => {
+    const newErrors: Record<string, string> = {}
+    if (!form.username.trim()) {
+      newErrors.username = "用户名不能为空"
+    } else if (form.username.trim().length < 3) {
+      newErrors.username = "用户名长度不能少于 3 位"
+    }
+
+    if (!form.email.trim()) {
+      newErrors.email = "邮箱不能为空"
+    } else if (!/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(form.email.trim())) {
+      newErrors.email = "邮箱格式不正确"
+    }
+
+    if (!form.password) {
+      newErrors.password = "密码不能为空"
+    } else if (form.password.length < 8) {
+      newErrors.password = "密码长度不能少于 8 位"
+    }
+
+    setErrors(newErrors)
+    return Object.keys(newErrors).length === 0
+  }
+
+  const handleSave = async (e: React.FormEvent) => {
+    e.preventDefault()
+    if (!validate()) return
+
+    setSaving(true)
+    try {
+      await createUser({
+        ...form,
+        username: form.username.trim(),
+        nickname: form.nickname?.trim() || undefined,
+        email: form.email.trim(),
+      })
+      onClose()
+    } catch {
+      // Errors are already handled by context toast notifications
+    } finally {
+      setSaving(false)
+    }
+  }
+
+  return (
+    <Dialog open={isOpen} onOpenChange={(open) => !open && onClose()}>
+      <DialogContent className="max-w-md">
+        <DialogHeader>
+          <DialogTitle>新增用户</DialogTitle>
+          <DialogDescription>
+            直接创建一个本地密码登录的新账户。
+          </DialogDescription>
+        </DialogHeader>
+
+        <form onSubmit={handleSave} className="space-y-4 pt-2">
+          <div className="space-y-1.5">
+            <Label htmlFor="username">用户名</Label>
+            <Input
+              id="username"
+              value={form.username}
+              onChange={(e) => setForm((prev) => ({ ...prev, username: e.target.value }))}
+              placeholder="请输入用户名 (至少 3 位)"
+            />
+            {errors.username && (
+              <p className="text-xs text-destructive">{errors.username}</p>
+            )}
+          </div>
+
+          <div className="space-y-1.5">
+            <Label htmlFor="nickname">昵称 (选填)</Label>
+            <Input
+              id="nickname"
+              value={form.nickname}
+              onChange={(e) => setForm((prev) => ({ ...prev, nickname: e.target.value }))}
+              placeholder="请输入昵称"
+            />
+          </div>
+
+          <div className="space-y-1.5">
+            <Label htmlFor="email">邮箱</Label>
+            <Input
+              id="email"
+              type="email"
+              value={form.email}
+              onChange={(e) => setForm((prev) => ({ ...prev, email: e.target.value }))}
+              placeholder="请输入邮箱地址"
+            />
+            {errors.email && (
+              <p className="text-xs text-destructive">{errors.email}</p>
+            )}
+          </div>
+
+          <div className="space-y-1.5">
+            <Label htmlFor="password">密码</Label>
+            <Input
+              id="password"
+              type="password"
+              value={form.password}
+              onChange={(e) => setForm((prev) => ({ ...prev, password: e.target.value }))}
+              placeholder="请输入登录密码 (至少 8 位)"
+            />
+            {errors.password && (
+              <p className="text-xs text-destructive">{errors.password}</p>
+            )}
+          </div>
+
+          <div className="flex items-center justify-between rounded-lg border border-dashed p-3 bg-muted/10">
+            <div>
+              <div className="font-medium text-sm">启用账户</div>
+              <div className="text-xs text-muted-foreground">禁用后此账号将无法登录系统。</div>
+            </div>
+            <Switch
+              checked={form.is_active}
+              onCheckedChange={(checked) => setForm((prev) => ({ ...prev, is_active: checked }))}
+            />
+          </div>
+
+          <div className="flex items-center justify-between rounded-lg border border-dashed p-3 bg-muted/10">
+            <div>
+              <div className="font-medium text-sm">管理员权限</div>
+              <div className="text-xs text-muted-foreground">开启后此账号将拥有后台管理权限。</div>
+            </div>
+            <Switch
+              checked={form.is_admin}
+              onCheckedChange={(checked) => setForm((prev) => ({ ...prev, is_admin: checked }))}
+            />
+          </div>
+
+          <div className="flex justify-end gap-2 pt-2 border-t mt-2">
+            <Button variant="outline" type="button" onClick={onClose}>
+              取消
+            </Button>
+            <Button type="submit" disabled={saving} variant="secondary">
+              {saving ? "创建中..." : "创建"}
+            </Button>
+          </div>
+        </form>
+      </DialogContent>
+    </Dialog>
+  )
+}