feat(tui): add sidebar width configuration option

[skydg]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem

The TUI sidebar width is currently hardcoded to 42 characters. Users cannot customize it to fit their workflow.

Proposed Solution

Add a sidebar_width option to tui.json configuration:

{
  "sidebar_width": 50
}

Use Cases

• Users with wide monitors want a larger sidebar for more content
• Users with narrow monitors want a smaller sidebar
• TUI plugin developers need more space for custom sidebar content
• Accessibility needs for different font sizes

Implementation Notes

• Default value: 42 (current behavior, no breaking change)
• Min value: 30
• Max value: 80
• Auto-adjust when terminal is too narrow

Related

This would also benefit TUI plugin developers who add custom sidebar content (buttons, status panels, etc.)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Is it possible to make the width of the sidebar configurable? #6087: "Is it possible to make the width of the sidebar configurable?" — directly requests the same configurable TUI sidebar width feature
• [FEATURE]: Add tui.json option to control content area max-width / horizontal padding #25142: "[FEATURE]: Add tui.json option to control content area max-width / horizontal padding" — related request for TUI layout width configuration via tui.json

If your request is covered by one of these, consider adding a comment there instead.