feat: 实现 Mock 支付功能，修复支付激活会员问题

- 当未配置 ALIPAY_* 环境变量时，自动启用 Mock 支付模式
- Mock 支付页面点击按钮后调用 /api/payment/mock-confirm 激活会员
- 更新 AGENTS.md 文档说明 Mock 支付配置和使用方法

Cargo.lock

@@ -405,9 +405,9 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.2.35"
+version = "1.2.61"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "590f9024a68a8c40351881787f1934dc11afd69090f5edb6831464694d836ea3"
+checksum = "d16d90359e986641506914ba71350897565610e87ce0ad9e6f28569db3dd5c6d"
 dependencies = [
  "find-msvc-tools",
  "jobserver",
@@ -689,9 +689,9 @@ checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
 
 [[package]]
 name = "find-msvc-tools"
-version = "0.1.0"
+version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e178e4fba8a2726903f6ba98a6d221e76f9c12c650d5dc0e6afdc50677b49650"
+checksum = "5baebc0774151f905a1a2cc41989300b1e6fbb29aff0ceffa1064fdd3088d582"
 
 [[package]]
 name = "flate2"