refactor(api): unify error handling and split upload/oauth god modules

Replace c.JSON(200, response.Err) and middleware gin.H bypasses with
response.Abort* helpers so errors flow through Gin Error chain and
ErrorHandlerMiddleware for OTel trace correlation.

Split oauth/sources.go into domain-focused files and decompose upload
into handler/filesrv/stats/task/cache/storage/util subpackages with a
root facade preserving existing import paths.

internal/common/response/abort.go

@@ -0,0 +1,45 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package response
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// AbortBadRequest 以 400 中断请求并将错误挂载到 Gin Error 链，供全局中间件统一记录 Trace 并响应。
+func AbortBadRequest(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusBadRequest, msg)
+}
+
+// AbortUnauthorized 以 401 中断请求并将错误挂载到 Gin Error 链。
+func AbortUnauthorized(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusUnauthorized, msg)
+}
+
+// AbortForbidden 以 403 中断请求并将错误挂载到 Gin Error 链。
+func AbortForbidden(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusForbidden, msg)
+}
+
+// AbortNotFound 以 404 中断请求并将错误挂载到 Gin Error 链。
+func AbortNotFound(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusNotFound, msg)
+}
+
+// AbortInternal 以 500 中断请求并将错误挂载到 Gin Error 链。
+func AbortInternal(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusInternalServerError, msg)
+}
+
+// AbortTooManyRequests 以 429 中断请求并将错误挂载到 Gin Error 链。
+func AbortTooManyRequests(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusTooManyRequests, msg)
+}
+
+// AbortConflict 以 409 中断请求并将错误挂载到 Gin Error 链。
+func AbortConflict(c *gin.Context, msg string) {
+	AbortWithError(c, http.StatusConflict, msg)
+}

internal/common/response/middleware.go

@@ -0,0 +1,40 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package response
+
+import (
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	"go.opentelemetry.io/otel/codes"
+	"go.opentelemetry.io/otel/trace"
+)
+
+// ErrorHandlerMiddleware 捕获 c.Errors 并统一格式化为 JSON 返回给客户端，同时将其记录到 Span 异常中。
+// 与 AbortWithError / AbortBadRequest 等配合使用，是全局 OTel 友好错误响应的唯一出口。
+func ErrorHandlerMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.Next()
+
+		if len(c.Errors) == 0 || c.Writer.Written() {
+			return
+		}
+
+		err := c.Errors.Last().Err
+		span := trace.SpanFromContext(c.Request.Context())
+		if span.IsRecording() {
+			span.RecordError(err)
+			span.SetStatus(codes.Error, err.Error())
+		}
+
+		var apiErr *APIError
+		if errors.As(err, &apiErr) {
+			c.JSON(apiErr.Code, Err(apiErr.Msg))
+			return
+		}
+
+		c.JSON(http.StatusInternalServerError, Err("内部系统错误"))
+	}
+}