feat(C-04)：AI图片放大最小闭环

新应用aitool：POST /api/aitool/upscale（登录扣2积分、事务行锁防并发超扣，失败退款+failed记录）；产物存MEDIA_ROOT/aitool/upscale，返回可下载URL；provider默认本地Pillow，第三方网关走环境变量不落库。

aitool/admin.py

@@ -0,0 +1,12 @@
+from django.contrib import admin
+
+from .models import AIToolRecord
+
+
+@admin.register(AIToolRecord)
+class AIToolRecordAdmin(admin.ModelAdmin):
+    list_display = ['tool', 'user', 'status', 'cost', 'scale', 'created_at']
+    list_filter = ['tool', 'status', 'created_at']
+    search_fields = ['user__username']
+    ordering = ['-created_at']
+    readonly_fields = ['created_at']