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/apps/upload/shared/constants.go

@@ -0,0 +1,23 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package shared
+
+import "github.com/Rain-kl/Wavelet/internal/storage"
+
+// Upload size, path, media quality, and cache constants shared across subpackages.
+const (
+	MaxUploadSize      = 32 * 1024 * 1024 // 32MB
+	DetectContentBytes = 512              // http.DetectContentType 需要的最小字节数
+	UploadDirPerm      = 0755             // 上传目录权限
+	UploadFilePerm     = 0644             // 上传文件权限
+	ImageQualityLow    = "low"
+	ImageQualityMedium = "medium"
+	ImageQualityHigh   = "high"
+	ImageQualityOrigin = "origin"
+	StorageDriverLocal = string(storage.DriverLocal)
+	DefaultPublicUploadType = "avatar"
+	FileStatsTrendDays      = 7
+	MaxS3KeyLength          = 1024
+	AccessCacheTTL          = 5 // seconds; multiplied by time.Second at use site
+)

internal/apps/upload/shared/errs.go

@@ -0,0 +1,41 @@
+// Copyright 2025 linux.do
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+// Package shared holds upload error and configuration constants shared across subpackages.
+package shared
+
+// 文件管理常量
+const (
+	ErrNoFileSelected                  = "请选择要上传的文件"
+	ErrUnsupportedFormat               = "只支持 JPG、PNG、WEBP 格式的图片"
+	ErrProcessFileFailed               = "处理文件失败"
+	ErrSaveFileFailed                  = "保存文件失败"
+	ErrOpenFileFailed                  = "打开文件失败"
+	ErrSaveUploadRecordFailed          = "保存上传记录失败"
+	ErrGenericFileTooLarge             = "文件大小不能超过 32MB"
+	ErrFileContentExtensionMismatch    = "文件内容与扩展名不匹配，可能包含安全风险"
+	ErrFileValidationFailed            = "文件校验失败"
+	ErrInvalidMetadataJSON             = "元数据 JSON 格式不合法"
+	ErrInvalidFileID                   = "无效的文件 ID"
+	ErrQueryUploadRecordFailed         = "查询文件记录失败"
+	ErrInvalidBatchDownloadRequest     = "参数绑定失败，请传入有效的文件 ID 数组"
+	ErrInvalidIDValueFormat            = "无效的 ID 值: %s"
+	ErrRetrieveUploadRecordsFailed     = "检索文件记录失败"
+	ErrNoValidFilesForArchive          = "没有找到任何有效的文件记录进行打包"
+	ErrInvalidParams                   = "参数错误"
+	ErrQueryFileCountFailed            = "查询文件数量失败"
+	ErrQueryFileListFailed             = "查询文件列表失败"
+	ErrDeleteFileFailed                = "删除文件失败"
+	ErrStorageReadOnly                 = "存储迁移维护中，当前仅允许读取文件"
+	ErrS3KeyRequired                   = "s3 key must not be empty"
+	ErrS3KeyTooLongFormat              = "s3 key exceeds maximum length of %d"
+	ErrS3KeyStartsWithSlash            = "s3 key must not start with /"
+	ErrS3KeyContainsNullBytes          = "s3 key must not contain null bytes"
+	ErrQueryUnusedUploadsFailed        = "查询未使用的上传文件失败: %w"
+	ErrImageCacheWarmupPayloadRequired = "图片缓存预热参数不能为空"
+	ErrInvalidImageCacheWarmupPayload  = "图片缓存预热参数格式无效: %w"
+	ErrInvalidImageCacheWarmupQuality  = "图片质量仅支持 low、medium、high"
+	ErrParseImageCacheWarmupPayload    = "解析图片缓存预热参数失败: %w"
+	ErrQueryImagesForCacheWarmup       = "查询待预热图片失败: %w"
+)