Add Copy Path to the session context menu

[jsgrrchg]

Summary

• Add a Copy Path action to the desktop session context menu.
• Prefer the host-resolved Git checkout root when it matches the current working directory, with the current absolute working directory as a safe fallback.
• Support remote sessions by copying the path in the host device filesystem namespace without requiring an RPC.
• Hide the action when no absolute checkout path is available, including projectless sessions that use ~.

UX note

Copy Path is intentionally silent: it writes to the clipboard and closes the menu without showing a confirmation banner. If you prefer it to not be silent, let me know.

The existing copy items use sidebar_notice for confirmation. In normal use, those banners disappear only when the user clicks them; they do not currently have a timeout. The component also appears to have been designed primarily for error handling, as indicated by its persistent danger styling. A follow-up should consider giving these confirmation banners a timeout or introducing a dedicated transient success notification.

Testing

• cargo test -p zeron-ui copy_path
• git diff --check

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