9e982a8eb1
Add proposal, design, specs and tasks for the fix-timezone-double-conversion change. Documents the root cause (icsDateToJsDate returning fake UTC causing double browser offset), the Intl.DateTimeFormat-based solution, and 40+ test scenarios covering DST, cross-timezone, half-hour offsets, and round-trip conversions. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>