Add desktop workspace copy and switch action

[yiqi-017]

Summary

• Add a desktop settings action to copy the current GA workspace to a user-selected parent directory and switch the bridge to the copied workspace.
• Verify the restarted bridge reports the expected ga_root before showing success, and roll back the saved override if switching fails.
• Keep the bundled runtime intact, avoid compatibility probing for self-copied workspaces, and normalize Windows paths before passing them to Python.

Test plan

• Ran cargo check in frontends/desktop/src-tauri.
• Built Windows portable package from the feature branch and extracted it locally to C:\Users\Hp\Desktop\TEST_GA.
• Confirmed GenericAgent.exe exists in the extracted portable package.