refactor(desktop): separate shared sessions from Runtime Host profiles

[M4n5ter]

Summary

English

Separate shared-Session Guest connections from normal Runtime Host profiles. A collaboration invitation now creates a bounded, credential-backed Guest mount with its own reconnect and removal lifecycle, so it cannot alter default-Host preferences or leave pairing recovery state behind.

This is the first PR in the Runtime Host connectivity lifecycle stack.

中文

将共享 Session 的 Guest 连接从普通 Runtime Host profile 中分离。协作邀请现在创建独立、数量受限且由凭据存储支撑的 Guest mount，并拥有自己的重连和移除生命周期，因此不会修改默认 Host 偏好，也不会遗留配对恢复状态。

这是 Runtime Host 连接生命周期重做 stack 的第一个 PR。

Refs #3843

Verification

English

• Runtime Host and affected Desktop TypeScript builds pass.
• Focused Guest mount and Desktop Runtime Host manager suites pass.
• High-value coverage verifies restart rehydration, same-Root Owner/Guest startup, failure cleanup, and durable unmount before connection teardown.

中文

• Runtime Host 与受影响的 Desktop TypeScript 构建通过。
• Guest mount 与 Desktop Runtime Host manager 聚焦测试通过。
• 高价值测试覆盖重启恢复、同一 Root 的 Owner/Guest 启动、失败清理，以及先持久移除再关闭连接。

Review focus

Guest credentials and Session authority remain resource-scoped; this path must never re-enter normal profile preferences, pairing journals, or default-Host selection.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: OpenAI Codex — architecture planning, implementation, focused tests, and review.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[jackwener]

Approved at the explicit direction of M4n5ter. No technical review was performed as part of this action; M4n5ter requested the approval and accepts responsibility for subsequent handling.

---

Review notice: This approval was submitted by an automated review agent operated by jackwener and is published at the direction of M4n5ter, who is the human accountable for it.