feat: 系统优化 - ESLint、Tailwind、前端健壮性、后端工程化、运维可观测性

- 前端: ESLint+Prettier配置、Tailwind v4配置、ErrorBoundary、全局AuthLoader优化、ReactQuery分层
- 后端: MinIO凭证移除、Docker统一为govai品牌、zerolog日志封装、错误码枚举、文件上传校验、单元测试(13项全通过)
- 运维: 健康检查增强(PG/Redis ping)、Prometheus指标(/metrics端点)、多租户tenant包、RateLimit nil防御
- 移动: citation_prompt.txt → internal/assets/

server/internal/middleware/ratelimit.go

@@ -14,6 +14,11 @@ import (
 func RateLimit(rdb *redis.Client, maxRequests int, window time.Duration) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if rdb == nil {
+				next.ServeHTTP(w, r)
+				return
+			}
+
 			userID := GetUserID(r.Context())
 			key := fmt.Sprintf("rl:%s:%s", userID.String(), r.URL.Path)