Installer self-update robustness and logging improvements

What Changed

Installer never bricks on self-update swap failure; post-update relaunch/install target derivation now covered; LogStream properly passed to emit_log calls; stdout-style progress no longer mislabeled as stderr; Windows update handles dirty worktree; macOS self-update rebuilds and relaunches cleanly.

Operator Implication

Critical for automated deployment pipelines: self-updates are now safer and more robust. Windows and macOS users should experience cleaner update cycles. Logging improvements aid troubleshooting.

Receipt

• Commits June 3: d3b1e43 'fix(installer): never brick the install when a self-update swap fails'; 39fee4f 'test(installer): cover the post-update relaunch/instal