Add comprehensive implementation plan for UI fixes

Consolidated analysis from 11 sub-agents covering:
- 5 screenshot analyses identifying visual issues
- 6 issue investigations with root cause analysis

Plan covers 6 implementation phases:
1. Foundation - Craft.do style CSS variables
2. User Messages - Collapsible cells, text wrapping
3. Toggle System - shadcn-style tabs
4. Collapsibility Unification - Sticky cascade, <details> everywhere
5. Copy System - Format indicators, view mode respect
6. Specialized Tools - Toggles for Write/Edit/Bash/TodoWrite

Includes parallel execution matrix, test plan, and known risks.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ShlomoStept