feat: 实现统一错误处理系统 (003-error-handling)

- 新增统一错误码定义和管理 (pkg/errors/codes.go)
- 新增全局错误处理器和中间件 (pkg/errors/handler.go, internal/middleware/error_handler.go)
- 新增错误上下文管理 (pkg/errors/context.go)
- 增强 Panic 恢复中间件 (internal/middleware/recover.go)
- 新增完整的单元测试和集成测试
- 新增功能文档 (docs/003-error-handling/)
- 新增功能规范 (specs/003-error-handling/)
- 更新 CLAUDE.md 和 README.md

.specify/templates/tasks-template.md

@@ -207,6 +207,18 @@ Foundational tasks for 君鸿卡管系统 tech stack:
 - [ ] TXXX Quality Gate: Verify logging via centralized Logger middleware (pkg/logger/Middleware())
 - [ ] TXXX Quality Gate: Verify no middleware bypasses logging (test auth failures, rate limits, etc.)
 - [ ] TXXX Quality Gate: Verify access log has all required fields (method, path, query, status, duration_ms, request_id, ip, user_agent, user_id, request_body, response_body)
+- [ ] TXXX Quality Gate: Verify all API errors use unified JSON format (pkg/errors/ ErrorHandler)
+- [ ] TXXX Quality Gate: Verify Handler layer returns errors (no manual c.Status().JSON() for errors)
+- [ ] TXXX Quality Gate: Verify business errors use pkg/errors.New() or pkg/errors.Wrap()
+- [ ] TXXX Quality Gate: Verify all error codes defined in pkg/errors/codes.go
+- [ ] TXXX Quality Gate: Verify Recover middleware catches all panics
+- [ ] TXXX Quality Gate: Verify error logs include request context (Request ID, path, method)
+- [ ] TXXX Quality Gate: Verify 5xx errors auto-sanitized (no sensitive info exposed)
+- [ ] TXXX Quality Gate: Verify no panic in business code (search for panic() calls)
+- [ ] TXXX Quality Gate: Verify error codes follow classification (0=success, 1xxx=4xx, 2xxx=5xx)
+- [ ] TXXX Quality Gate: Verify Recover middleware registered first in chain
+- [ ] TXXX Quality Gate: Test panic recovery logs complete stack trace
+- [ ] TXXX Quality Gate: Test single request panic doesn't affect other requests
 
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