feat: 渠道展示、订阅套餐、系统配置全功能

- 新增 Channel / SubscriptionPlan / SystemConfig 三个数据模型
- Order 模型扩展支持订阅订单（order_type, plan_id, subscription_group_id）
- Sub2API client 新增分组查询、订阅分配/续期、用户订阅查询
- 订单服务支持订阅履约流程（CAS 锁 + 分组消失安全处理）
- 管理后台：渠道管理、订阅套餐管理、系统配置、Sub2API 分组同步
- 用户页面：双 Tab UI（按量付费/包月订阅）、渠道卡片、充值弹窗、订阅确认
- PaymentForm 支持 fixedAmount 固定金额模式
- 订单状态 API 返回 failedReason 用于订阅异常展示
- 数据库迁移脚本

src/app/api/admin/subscription-plans/route.ts

@@ -0,0 +1,89 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { verifyAdminToken, unauthorizedResponse } from '@/lib/admin-auth';
+import { prisma } from '@/lib/db';
+import { getGroup } from '@/lib/sub2api/client';
+
+export async function GET(request: NextRequest) {
+  if (!(await verifyAdminToken(request))) return unauthorizedResponse(request);
+
+  try {
+    const plans = await prisma.subscriptionPlan.findMany({
+      orderBy: { sortOrder: 'asc' },
+    });
+
+    // 并发检查每个套餐对应的 Sub2API 分组是否仍然存在
+    const results = await Promise.all(
+      plans.map(async (plan) => {
+        let groupExists = false;
+        try {
+          const group = await getGroup(plan.groupId);
+          groupExists = group !== null;
+        } catch {
+          groupExists = false;
+        }
+        return {
+          ...plan,
+          price: Number(plan.price),
+          originalPrice: plan.originalPrice ? Number(plan.originalPrice) : null,
+          groupExists,
+        };
+      }),
+    );
+
+    return NextResponse.json({ plans: results });
+  } catch (error) {
+    console.error('Failed to list subscription plans:', error);
+    return NextResponse.json({ error: '获取订阅套餐列表失败' }, { status: 500 });
+  }
+}
+
+export async function POST(request: NextRequest) {
+  if (!(await verifyAdminToken(request))) return unauthorizedResponse(request);
+
+  try {
+    const body = await request.json();
+    const { group_id, name, description, price, original_price, validity_days, features, for_sale, sort_order } = body;
+
+    if (!group_id || !name || price === undefined) {
+      return NextResponse.json({ error: '缺少必填字段: group_id, name, price' }, { status: 400 });
+    }
+
+    // 验证 group_id 唯一性
+    const existing = await prisma.subscriptionPlan.findUnique({
+      where: { groupId: Number(group_id) },
+    });
+
+    if (existing) {
+      return NextResponse.json(
+        { error: `分组 ID ${group_id} 已被套餐「${existing.name}」使用` },
+        { status: 409 },
+      );
+    }
+
+    const plan = await prisma.subscriptionPlan.create({
+      data: {
+        groupId: Number(group_id),
+        name,
+        description: description ?? null,
+        price,
+        originalPrice: original_price ?? null,
+        validityDays: validity_days ?? 30,
+        features: features ?? null,
+        forSale: for_sale ?? false,
+        sortOrder: sort_order ?? 0,
+      },
+    });
+
+    return NextResponse.json(
+      {
+        ...plan,
+        price: Number(plan.price),
+        originalPrice: plan.originalPrice ? Number(plan.originalPrice) : null,
+      },
+      { status: 201 },
+    );
+  } catch (error) {
+    console.error('Failed to create subscription plan:', error);
+    return NextResponse.json({ error: '创建订阅套餐失败' }, { status: 500 });
+  }
+}