🐛 fix stale desktop lock recovery

[Yesec]

Summary

This fixes the desktop stale lock recovery path described in #32.

Changes:

• validate .rx.is.alive instead of exiting only because the file exists
• only treat a 2xx response from POST /popup as a live existing instance
• treat unreadable lock files, invalid port contents, failed requests, and non-2xx responses as stale state
• remove stale lock files and continue the current launch immediately
• add a best-effort cleanup path after ui.run() returns

Files changed

• crates/desktop/src/launcher.rs
• crates/desktop/src/main.rs

Validation

• cargo check --workspace

[Copilot]

Pull request overview

This PR improves the desktop “stale lock” recovery path so that a leftover .rx.is.alive no longer blocks startup when the prior instance is gone, and adds a best-effort cleanup path when the UI event loop returns.

Changes:

• Refactors lock-file handling to validate the stored port and only exit when a /popup request returns 2xx; otherwise the lock is treated as stale and removed.
• Adds runtime cleanup helpers and wires cleanup to run after ui.run() returns.
• Centralizes shutdown cleanup to reuse the same cleanup logic.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
crates/desktop/src/launcher.rs	Adds lock validation + “focus existing instance” logic; introduces cleanup helpers used by shutdown and post-ui.run() cleanup.
crates/desktop/src/main.rs	Calls new cleanup path after ui.run() returns, using a weak handle to the UI.

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[Reverier-Xu]

Closes #32 .