feat: Always display username@hostname in starship prompt

[maxrantil]

Summary

Configure starship to always display username and hostname (not just during SSH sessions) for better VM identification clarity.

Context

This change complements the vm-infra configurable username feature (maxrantil/vm-infra#117, PR maxrantil/vm-infra#118) where VMs are provisioned with:

• Configurable usernames (e.g., developer, testuser)
• VM names as hostnames (e.g., work-vm-1, test-vm-2)

Problem: Default starship config only shows username during SSH sessions. When working with multiple VMs, it's hard to identify which VM you're in.

Solution: Always show username@hostname in the prompt for immediate context.

Changes

starship.toml

• ✅ Added [username] section with show_always = true
  • Yellow for regular users
  • Red for root (warning indicator)
• ✅ Added [hostname] section with ssh_only = false
  • Green color with @ prefix
  • Trim domain suffix (.local)
• ✅ Updated format string to include $username$hostname

Result

Before:

~/projects
❯

After:

┌───────────────────>
│developer@work-vm-1~/projects main
└─>❯

Benefits

Multi-VM Clarity:

• developer@work-vm-1 vs developer@work-vm-2 - instantly clear which VM
• testuser@test-vm vs developer@prod-vm - context at a glance
• Works in all contexts (SSH, console, tmux)

Security:

• Root user shown in red - immediate warning
• No ambiguity about current user context

Testing

Tested with vm-infra's --test-dotfiles flag:

./provision-vm.sh test-vm testuser 2048 1 --test-dotfiles /path/to/dotfiles

Expected prompt: testuser@test-vm ~/path

References

• vm-infra Issue: feat: Add configurable username parameter to VM provisioning vm-infra#117
• vm-infra PR: feat: Add configurable username and VM-based hostname vm-infra#118
• Implementation Guide: STARSHIP_CONFIG_NOTE.md in vm-infra repo
• Starship Docs: https://starship.rs/config/#username

---

Ready for review - Simple config change, well-documented, tested with vm-infra integration.