chore: baseline snapshot before moderation-strictness feature

Repo .git was damaged (refs/ missing, index truncated, object store near-empty).
Repaired via git init (rebuilt refs), stale index preserved as .git/index.corrupt-20260910.bak,
then full worktree committed as a rollback baseline.

dev/s3stub/s3_stub.go

@@ -0,0 +1,31 @@
+// s3_stub.go 是 internal/storage/s3.go 的本地编译桩：s3.go 依赖 cgo 库
+// chai2010/webp（需要 libwebp + C 工具链），Windows 沙箱无此环境。
+// 通过 `go build -overlay=dev/overlay.json` 用本文件替换 s3.go，做全模块类型检查。
+// 符号覆盖 = s3.go 中被包内其他文件（oss.go 引用 isSupportedImage）与
+// 包外调用方（route/user、route/question、route/chat 等）引用的全部标识符。
+// 桩仅在类型检查时生效，不会被真正调用；生产构建在 Linux（cgo + libwebp）下不受影响。
+package storage
+
+import (
+	"io"
+	"mime/multipart"
+)
+
+// MaxUploadBytes 与真实实现保持一致（8MB 单图上限，bodylimit 中间件依赖此值语义）。
+const MaxUploadBytes = 8 * 1024 * 1024
+
+func UploadPictureToS3(file multipart.File, fileHeader *multipart.FileHeader) (string, error) {
+	return "", nil
+}
+
+func UploadAvatarToS3(file multipart.File, fileHeader *multipart.FileHeader) (string, error) {
+	return "", nil
+}
+
+func UploadBackgroundToS3(file multipart.File, fileHeader *multipart.FileHeader) (string, error) {
+	return "", nil
+}
+
+func ConvertStaticImageToWebP(r io.Reader) ([]byte, error) { return nil, nil }
+
+func isSupportedImage(data []byte) bool { return true }