Allow resuming a session from a different working directory

Currently, claude --resume <id> requires you to be in the same directory the session was started in, or it fails with a "session does not exist" error. This makes it impossible to move a session to a new folder or resume it from a different context.

Requested behavior: claude --resume <id> should work from any directory.

Additional UX: In the session list (-r / session picker), after pressing Ctrl+A and selecting on a session should allow opening it in a new folder, so the user can relocate a session interactively.

Use case: I had an active session in folder A and wanted to continue it in folder B (e.g., after reorganizing a project). There is currently no way to do this without manually copying context.