refactor(link)!: consolidate borrowing and terminal ownership

[nostalume]

Summary / 摘要

• Consolidate Domain 1 link acquisition and terminal ownership: cache entries return isolated borrowers, while proxy and seekable-stream consumers own link cleanup.

• Release range bodies before their links, including chunk reads; remove the duplicate lifecycle-policy file, ProxyRange, redundant link wrappers, and caller-side cleanup.

• Preserve range/HEAD behavior and cached descriptor isolation with behavior tests. Relative to 893457cd, production Go code is net -23 lines and tests are net +112 lines.

• Compatibility: the exported server/common.Proxy function now takes a proxyRange bool argument. All in-repository callers are updated; external Go callers of this function must pass the new argument. No config or storage-format migration is required.

• This PR has breaking changes.
  / 此 PR 包含破坏性变更。

• This PR changes public API, config, storage format, or migration behavior.
  / 此 PR 修改了公开 API、配置、存储格式或迁移行为。

• This PR requires corresponding changes in related repositories.
  / 此 PR 需要关联仓库同步修改。

Related repository PRs / 关联仓库 PR: None known.

Related Issues / 关联 Issue

Relates to #3098.

Testing / 测试

• go test ./... — run on Windows with Go 1.27.1, but not passing. The same upstream base also fails in the same categories: pre-existing dynamic-format vet errors and environment-sensitive package tests (onedrive_sharelink, multipart, internal/net, aria2/rpc, server/mcp). This PR does not claim a green full suite.
• Manual test / 手动测试: not performed.
• Passed on Windows/Go 1.27.1: go build ./... and fresh focused go test -count=1 for the changed packages (internal/model, internal/op, internal/stream, internal/fs, internal/offline_download/tool, server/common, server/handles, server/webdav, server/ftp, drivers/alias, drivers/chunk, drivers/crypt, drivers/strm).
• Passed on WSL Tumbleweed/Go 1.27.1: go test -race -count=1 ./internal/op ./internal/stream ./server/common ./drivers/chunk ./drivers/strm (the chunk package currently has no tests).
• git diff --check, committed-file gofmt check, and Git connectivity fsck passed.

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。

AI Disclosure / AI 使用声明

• This PR includes AI-assisted content.
  / 此 PR 包含 AI 辅助内容。

Tools used / 使用工具:

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Usage scope / 使用范围:

• Code generation / 代码生成

• Refactoring / 重构

• Documentation / 文档

• Tests / 测试

• Translation / 翻译

• Review assistance / 审查辅助

• I have reviewed and validated all AI-assisted content included in this PR.
  / 我已审核并验证此 PR 中包含的所有 AI 辅助内容。

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  / 我已确保所有 AI 辅助提交都包含归属信息。

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  / 我可以在没有任何 AI 工具的情况下重现此 PR 中包含的所有 AI 辅助内容。

This draft remains pending the contributor's own review and policy attestations; the unchecked boxes are intentional.