[UX] Expandable/collapsible content for long output

[randomm]

Inspiration

Claude Code collapses long output:

… +9 lines (ctrl+o to expand)
+5 more tool uses (ctrl+o to expand)

Benefit

• Keeps UI clean when lots of tools run
• User can expand to see details if needed
• Reduces visual noise

Implementation

• When tool output exceeds N lines, show collapsed
• Add keyboard shortcut to expand (ctrl+o or similar)
• Track expanded/collapsed state per tool

Priority

Low — nice to have, complex to implement