UX: Improve vix -h help output indentation

Problem

The global help output is visually aligned to the far left, making it harder to scan.

Proposal

Introduce consistent indentation:

• 1 level for sections
• 2+ levels for sub-sections and entries

Acceptance criteria

• Consistent left padding across:
  • Usage
  • Commands
  • Options
  • Environment
  • Examples
• No regression in vix help <command>