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/lib/system-config.ts

@@ -0,0 +1,119 @@
+import { prisma } from '@/lib/db';
+
+// 内存缓存：key → { value, expiresAt }
+const cache = new Map<string, { value: string; expiresAt: number }>();
+const CACHE_TTL_MS = 30_000; // 30 秒
+
+function getCached(key: string): string | undefined {
+  const entry = cache.get(key);
+  if (!entry) return undefined;
+  if (Date.now() > entry.expiresAt) {
+    cache.delete(key);
+    return undefined;
+  }
+  return entry.value;
+}
+
+function setCache(key: string, value: string): void {
+  cache.set(key, { value, expiresAt: Date.now() + CACHE_TTL_MS });
+}
+
+export function invalidateConfigCache(key?: string): void {
+  if (key) {
+    cache.delete(key);
+  } else {
+    cache.clear();
+  }
+}
+
+export async function getSystemConfig(key: string): Promise<string | undefined> {
+  const cached = getCached(key);
+  if (cached !== undefined) return cached;
+
+  const row = await prisma.systemConfig.findUnique({ where: { key } });
+  if (row) {
+    setCache(key, row.value);
+    return row.value;
+  }
+
+  // 回退到环境变量
+  const envVal = process.env[key];
+  if (envVal !== undefined) {
+    setCache(key, envVal);
+  }
+  return envVal;
+}
+
+export async function getSystemConfigs(keys: string[]): Promise<Record<string, string>> {
+  const result: Record<string, string> = {};
+  const missing: string[] = [];
+
+  for (const key of keys) {
+    const cached = getCached(key);
+    if (cached !== undefined) {
+      result[key] = cached;
+    } else {
+      missing.push(key);
+    }
+  }
+
+  if (missing.length > 0) {
+    const rows = await prisma.systemConfig.findMany({
+      where: { key: { in: missing } },
+    });
+
+    const dbMap = new Map(rows.map((r) => [r.key, r.value]));
+
+    for (const key of missing) {
+      const val = dbMap.get(key) ?? process.env[key];
+      if (val !== undefined) {
+        result[key] = val;
+        setCache(key, val);
+      }
+    }
+  }
+
+  return result;
+}
+
+export async function setSystemConfig(key: string, value: string, group?: string, label?: string): Promise<void> {
+  await prisma.systemConfig.upsert({
+    where: { key },
+    update: { value, ...(group !== undefined && { group }), ...(label !== undefined && { label }) },
+    create: { key, value, group: group ?? 'general', label },
+  });
+  invalidateConfigCache(key);
+}
+
+export async function setSystemConfigs(configs: { key: string; value: string; group?: string; label?: string }[]): Promise<void> {
+  await prisma.$transaction(
+    configs.map((c) =>
+      prisma.systemConfig.upsert({
+        where: { key: c.key },
+        update: { value: c.value, ...(c.group !== undefined && { group: c.group }), ...(c.label !== undefined && { label: c.label }) },
+        create: { key: c.key, value: c.value, group: c.group ?? 'general', label: c.label },
+      }),
+    ),
+  );
+  invalidateConfigCache();
+}
+
+export async function getSystemConfigsByGroup(group: string): Promise<{ key: string; value: string; label: string | null }[]> {
+  return prisma.systemConfig.findMany({
+    where: { group },
+    select: { key: true, value: true, label: true },
+    orderBy: { key: 'asc' },
+  });
+}
+
+export async function getAllSystemConfigs(): Promise<{ key: string; value: string; group: string; label: string | null }[]> {
+  return prisma.systemConfig.findMany({
+    select: { key: true, value: true, group: true, label: true },
+    orderBy: [{ group: 'asc' }, { key: 'asc' }],
+  });
+}
+
+export async function deleteSystemConfig(key: string): Promise<void> {
+  await prisma.systemConfig.delete({ where: { key } }).catch(() => {});
+  invalidateConfigCache(key);
+}