chore: 将后端移动到 api/ 目录，准备合并为单仓库

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

api/account/admin.py

@@ -0,0 +1,24 @@
+from django.contrib import admin
+from django.contrib.auth.admin import UserAdmin
+from django.contrib.auth.models import Group
+from .models import User
+
+admin.site.site_header = "前端开发网站管理"
+admin.site.site_index = "前端开发网站管理"
+admin.site.site_title = "前端开发网站管理"
+
+admin.site.unregister(Group)
+
+
+@admin.register(User)
+class AdminAccount(UserAdmin):
+    fieldsets = ((None, {"fields": ("username", "password", "role", "is_active")}),)
+    add_fieldsets = (
+        (
+            None,
+            {"fields": ("username", "password1", "password2", "role")},
+        ),
+    )
+    list_display = ("username", "role", "is_active")
+    list_filter = ("role", "is_active")
+    search_fields = ("username",)