文件上传：R2 对象存储 + 后台文件管理 + 编辑器/封面联动

存储抽象（internal/storage，新包）
- BlobStore 接口（Put / Open / Delete）+ 两个实现：R2（aws-sdk-go-v2 走
  R2 的 S3 兼容 API，path-style、region auto）与本地磁盘（DataDir/uploads，
  零配置兜底）。选择：Endpoint / S3Api / Bucket / AccessKey / SecretAccessKey
  齐全 → R2，缺任一项回落本地并在启动日志提示缺失的字段名（只报名字不报值）
- 端点 URL 里的路径段不交给 SDK：path-style 下它会被折进对象 key，
  导致「数据库 key」和「实际对象 key」对不上（直链 404，实测复现）。
  EndpointKeyPrefix 提取路径段给上传 handler 拼进 key，StripEndpointPath
  只取 scheme://host 给 SDK——数据库 / 存储端 / 直链三方一致

数据与 API
- files 表：id / key(唯一) / name / mime / size / sha256 / store(r2|local) /
  created_at；URL 不入库，按「store 来源 + PublicBase」响应时解析，
  切存储端不破坏存量链接
- POST /api/admin/files：multipart 多文件，单文件 ≤50MB（MaxBytesReader 64MB）；
  类型白名单 = 图片（jpg/png/webp/gif/avif）+ 附件（pdf/zip/txt），
  扩展名 + http.DetectContentType 双重校验（实测拦截随机字节改名 .png），
  SVG 拒绝（同源脚本）；内容 sha256 做 key（2026/09/{哈希前12位}{扩展名}），
  同内容重复上传自动去重复用
- GET /api/admin/files（分页 + 文件名搜索）、DELETE /{id}（先删对象再删行，
  存储端失败保留行可重试）
- 公开路由 GET /uploads/{key}（main.go 挂载）：按 key 查行、存储层流式返回，
  Cache-Control immutable + ETag 304；R2 + PublicBase 时 302 直链（后端不出流量）
- URL 解析：FileURL(store, key, PublicBase)——R2 且配了公开域名走直链，
  否则 /uploads/ 流式

后台文件管理页（FilesView，「工作台 → 文件」）
- 点击 / 拖拽多选上传（uploadFiles 走 FormData 裸 fetch，401 广播与
  request() 一致）；缩略图卡片网格（图片出图、其他出类型占位）；
  复制链接（clipboard，非 https 回落 prompt）/ 打开 / 删除（确认提示）；
  分页、loading/empty 沿用既有模式

编辑器联动（EditorView）
- 封面：URL 输入框旁「上传」按钮，选图自动填 cover_url
- wysiwyg：Crepe ImageBlock 官方 onUpload 钩子——粘贴 / 拖拽 / 插图
  全部走上传，返回 URL 后由 Crepe 插节点
- Markdown 模式：插图弹层加「上传」按钮 + 编辑器粘贴 / 拖拽图片，
  上传后在原光标处插入 ![](url)（异步上传先记光标位，逐张追踪偏移）

.env.example
- 模板入库（无敏感值）：Endpoint = 公开访问域名（直链）、S3Api = 上传端点、
  Bucket / AccessKey / SecretAccessKey

验证
- 本地兜底全流程：上传 201、同内容去重复用、随机字节改名 .png 被
  内容嗅探拒绝、.svg 拒绝、公开路由 immutable 缓存头 + 内容一致、
  删除后存储与公开路由双清 404
- R2 真实链路（站主 .env）：上传 store=r2、直链 200（过程中定位并修复
  S3Api 路径段折进 key 导致的直链 404，见 EndpointKeyPrefix）
- 后端 go build/test/vet 全绿；前端构建通过

backend/go.sum

@@ -1,3 +1,39 @@
+github.com/aws/aws-sdk-go-v2 v1.47.1 h1:uOIZnp4PK3ZhKI0dNrJrhTEsLxbpXHTAJlwoS1pvAtw=
+github.com/aws/aws-sdk-go-v2 v1.47.1/go.mod h1:bttEH6JqnUL8LepvDVfdrds/fZ5bCIxzpe3abyUrhDU=
+github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.20 h1:GPRlPwz40I2B2VrBEASOA3Bi77NyeqejNLkifosX0rs=
+github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.7.20/go.mod h1:g7PNzKcsOKWb4fkSRBA7BZVAS6Y8IcxzN+nRohhQ1Q8=
+github.com/aws/aws-sdk-go-v2/config v1.33.6 h1:MBjkSTLczek/UgiK+EYPIoRTqE7gP8vtW3OFbFo7Nug=
+github.com/aws/aws-sdk-go-v2/config v1.33.6/go.mod h1:grRAFzdAZJrwcbasJRg2MPvIrVjtlfXllHssN6+E1JE=
+github.com/aws/aws-sdk-go-v2/credentials v1.20.6 h1:NpAFXCU7NzXNkdGK3zQTtsRJ+3v9tZQV0xcdRw8uBdw=
+github.com/aws/aws-sdk-go-v2/credentials v1.20.6/go.mod h1:mcZCoiPnyMvP8VMNbygNX5lLqSlkYJIMPODylQMurOk=
+github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.20.1 h1:8gALAAmacnIXh+z6VkdDanv4/IkG5APdg4DZLDTmLog=
+github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.20.1/go.mod h1:Z7IJhJU+poOdJjUR2wpyY21ossQ1XS/R3Lk9Msq5kM4=
+github.com/aws/aws-sdk-go-v2/internal/configsources v1.5.4 h1:CLq4+8UHCI+ZZYl/EuJxXovaIVN2xeeT8JV+dsApQ5E=
+github.com/aws/aws-sdk-go-v2/internal/configsources v1.5.4/go.mod h1:Wv4q5sAM04xAMkoOedxLx2inVf6K5FdxYp+A61L+q/0=
+github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.8.4 h1:dD4MR81I7YkpEBRk6UP9rocC2QnT3qVuXwzlYTtfGEs=
+github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.8.4/go.mod h1:EcXV1kAFd5XwSkDHlj94gnF3q5CkJyYiIJfH8N0VmrE=
+github.com/aws/aws-sdk-go-v2/internal/v4a v1.5.4 h1:7Wo47d/xn/7KttCSBd8EGYeZ7ULRFRkUHr6vkZPBzVQ=
+github.com/aws/aws-sdk-go-v2/internal/v4a v1.5.4/go.mod h1:tDB2IVC1xC3vX8o+6uRlzhTxP3g1b77CZXFX/oD2FnQ=
+github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.19 h1:bAdDl/HkGCcGPoe25ToSHEw23VIxt6CT5fLcg111BKg=
+github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.13.19/go.mod h1:KaUzbLxv4CeSxh6ZCl9B4m7CuFenS8kUEaDs+f/DQr4=
+github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.11.5 h1:/TYsZXdA8UTa+WCtCYSAJIr1vwl0+eho6TUgJGwFFO8=
+github.com/aws/aws-sdk-go-v2/service/internal/checksum v1.11.5/go.mod h1:qPqp1Uwd/BqdhPufv6oem9j5J7HNsgc2V22dUiDPn+s=
+github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.14.4 h1:29SvnfGhXjTl8ONxFwbj2rs6lbhiFXD2CgFQmbT/bXY=
+github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.14.4/go.mod h1:wm04I5DMuNVvZHFe/dHnUxincvNbbK7AiNBbYsQivek=
+github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.20.4 h1:pPiWfgeNxqluKEph7hvU88kuGKBPOWzO+Dk9t2zqqNs=
+github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.20.4/go.mod h1:YlwGoIUDG/3kBQbdNOVs/xKZ9J01G8e/6D1mRBj9uTk=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.113.4 h1:n6kO3OlBvnDEksQpvBLbAldjHwGlu8kErvhHJkhlaRY=
+github.com/aws/aws-sdk-go-v2/service/s3 v1.113.4/go.mod h1:9APRWGLFITKD+xzWSIyT9V7QV4bNlEuIieWlzXgGFlI=
+github.com/aws/aws-sdk-go-v2/service/signin v1.10.1 h1:DzCCWLzcIRQ77F3DEUljud7bEjTgFOIKXP52NmVRyhU=
+github.com/aws/aws-sdk-go-v2/service/signin v1.10.1/go.mod h1:xpo/geVldu8payT375WekctUzopG/hBU7miiqItMUlw=
+github.com/aws/aws-sdk-go-v2/service/sso v1.38.1 h1:Umtl/0YZhng4xndfW3lKJrYYP7NLEjI6bGXVomwLcs0=
+github.com/aws/aws-sdk-go-v2/service/sso v1.38.1/go.mod h1:rRD/dnm7q0HYE/I5TMaPgkWyyUGLcwuxHLABsLnQ3e0=
+github.com/aws/aws-sdk-go-v2/service/ssooidc v1.43.1 h1:orIWdNiLgzrhu/11RcPPKO/SBzUUymbUQuZbSPImghg=
+github.com/aws/aws-sdk-go-v2/service/ssooidc v1.43.1/go.mod h1:skwM/xsbR/1ReUTesv9BhpJp1VjajR7DWQnuVLwiXsQ=
+github.com/aws/aws-sdk-go-v2/service/sts v1.51.1 h1:0HOqZXRvMytH6bFHVIc0oJX07sZjfhz0zXtjs6gdE8s=
+github.com/aws/aws-sdk-go-v2/service/sts v1.51.1/go.mod h1:26zA0GhDrLo+yiLI2yXWxqB1PdsShfLikoI7GOEgugM=
+github.com/aws/smithy-go v1.28.1 h1:R/nXH00c8qcfCzQVELtRw+eLQWtzv+VAIEFJ1/xxXlQ=
+github.com/aws/smithy-go v1.28.1/go.mod h1:YE2RhdIuDbA5E5bTdciG9KrW3+TiEONeUWCqxX9i1Fc=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
 github.com/google/pprof v0.0.0-20250317173921-a4b03ec1a45e h1:ijClszYn+mADRFY17kjQEVQ1XRhq2/JR1M3sGqeJoxs=