feat: 插件化支付渠道限额 — provider 自声明单笔/每日默认限额

- PaymentProvider 接口新增 defaultLimits（单笔 singleMax + 每日 dailyMax）
- EasyPay 默认：支付宝/微信各 单笔 ¥1000、每日 ¥10000
- Stripe 默认：不限额（0 = unlimited）
- getMethodDailyLimit / getMethodSingleLimit 优先读 env var，再回退 provider 默认
- queryMethodLimits 返回 singleMax，PaymentForm 按渠道动态调整最大单笔金额
- MAX_DAILY_AMOUNT_* 改为可选 env var 覆盖（不再有硬编码默认值）

src/lib/payment/registry.ts

@@ -1,4 +1,4 @@
-import type { PaymentProvider, PaymentType } from './types';
+import type { PaymentProvider, PaymentType, MethodDefaultLimits } from './types';
 
 export class PaymentProviderRegistry {
   private providers = new Map<PaymentType, PaymentProvider>();
@@ -24,6 +24,12 @@ export class PaymentProviderRegistry {
   getSupportedTypes(): PaymentType[] {
     return Array.from(this.providers.keys());
   }
+
+  /** 获取指定渠道的提供商默认限额（未注册时返回 undefined） */
+  getDefaultLimit(type: string): MethodDefaultLimits | undefined {
+    const provider = this.providers.get(type as PaymentType);
+    return provider?.defaultLimits?.[type];
+  }
 }
 
 export const paymentRegistry = new PaymentProviderRegistry();

src/lib/payment/types.ts

@@ -51,10 +51,20 @@ export interface RefundResponse {
   status: 'success' | 'pending' | 'failed';
 }
 
+/** Per-method default limits declared by the provider */
+export interface MethodDefaultLimits {
+  /** 单笔最大金额，0 = 不限（使用全局 MAX_RECHARGE_AMOUNT） */
+  singleMax?: number;
+  /** 每日全平台最大金额，0 = 不限 */
+  dailyMax?: number;
+}
+
 /** Common interface that all payment providers must implement */
 export interface PaymentProvider {
   readonly name: string;
   readonly supportedTypes: PaymentType[];
+  /** 各渠道默认限额，key 为 PaymentType（如 'alipay'），可被环境变量覆盖 */
+  readonly defaultLimits?: Record<string, MethodDefaultLimits>;
 
   createPayment(request: CreatePaymentRequest): Promise<CreatePaymentResponse>;
   queryOrder(tradeNo: string): Promise<QueryOrderResponse>;