Release notes for version 2.1.217

Version 2.1.217 adds emoji shortcode autocomplete in the prompt input, improves transcript write warnings, and fixes numerous issues including memory leaks, Windows auto-update failures, session isolation problems, screen reader mode glitches, and subagent spawning controls. The release also enhances footer PR badge links, adjusts login expiry warnings, and caps concurrent subagents to prevent unbounded background agent creation.