fix(fs): clear skipped names before copy and move tasks

[Suyunmeng]

Summary / 摘要

• Fixed a bug in batch copy and move where skip_existing could still pass raw item names into task creation.
• Normalized each valid source entry to full source path before destination conflict checks in FsCopy and FsMove.
• Explicitly cleared skipped entries so the downstream task loop cannot consume stale raw names.
• User-visible behavior change: when skip_existing is enabled and destination already contains same-name objects, the request now skips correctly instead of triggering storage not found with rawPath.
• No breaking change.
• No public API, config, storage format, or migration change.

Related Issues / 关联 Issue

Fixes #2519

Testing / 测试

• go test ./...
• Targeted test: go test ./server/handles
• Targeted test: go test ./server/...
• Manual test / 手动测试:

Checklist / 检查清单

• I have read CONTRIBUTING.
  / 我已阅读 CONTRIBUTING。
• I confirm this contribution follows the repository license, contribution policy, and code of conduct.
  / 我确认此贡献符合仓库许可证、贡献规范和行为准则。
• I have formatted the changed code with gofmt, go fmt, or prettier where applicable.
  / 我已按适用情况使用 gofmt、go fmt 或 prettier 格式化变更代码。
• I have requested review from relevant maintainers or code owners where applicable.
  / 我已在适用情况下请求相关维护者或代码所有者审查。

[j2rong4cn]

我的锅，疏忽了