Modernize: make (as task runner)

[martinciu]

Evaluate adopting a modern task runner for ad-hoc project tasks. This is not about replacing make as a build system.

Candidate (re-evaluate at decision time)

• just — Justfile-based task runner

Decide

• Worth it only if there are recurring multi-step commands worth memorializing.
• If adopted: add to Brewfile, update CLAUDE.md and shell-colors cheatsheet.

Out of scope

• Don't replace make for actual builds.
• Don't bundle multiple tool swaps into one PR.