TUI: Detail pane with comments and scrolling

[mkoertgen]

Enhance issue detail pane to include comments and scrolling.

Scope:

• Load richer detail payload
• Render comments (author/date/body)
• Scroll behavior and readable formatting
• Empty-state and error handling

[mkoertgen]

Status update after commit bd404bc:\n\nPartially addressed:\n- Detail pane improved with issue type and parent/child hierarchy context\n\nStill open for this issue:\n- Render comments (author/date/body)\n- Scrollable comment/details view\n