Document quick workstation maintenance

[priithunt]

What changed

• present the quick read-only workstation status as the first operational view
• document the one-command Homebrew maintenance path and its no-op behavior
• retain the lower-level reviewed path for mixed Homebrew, mise, and Neovim maintenance

Why

The public snapshot should reflect the completed P0 usability work without exposing production repository details. Ordinary maintenance now has a concise path while strict and mixed workflows remain available when needed.

User impact

Readers get a clearer picture of how everyday two-Mac maintenance stays fast, reviewable, and free of unnecessary Git churn.

Validation

• private showcase allowlist and freshness check: 44 files passed
• deterministic public render completed
• scripts/verify-showcase.sh . passed
• public diff is limited to README.md, docs/maintenance.md, and docs/workflows.md