Improve visual styling and layout polish

[nicholasgcoles]

Summary

Polish the TUI's visual presentation to make tab groups easier to scan and status feedback clearer.

Tasks

• Add visual separators between project groups (currently just blank lines)
• Add per-project tab count in section headers (e.g. TabGate (3))
• Differentiate status messages by type (success=green, error=red, warning=orange)
• Add active project highlight (background or border for the group containing the cursor)
• Add scroll indicator when content exceeds viewport height
• Improve empty state with styled messaging
• Consider box-drawing borders for header/footer