Add loop-action subsection to QUICKSTART

[cobusgreyling]

Goal

Document the new loop-action composite action in QUICKSTART so CI adopters discover it next to the other npm tools.

Files

• docs/QUICKSTART.md — short subsection (inputs, one workflow snippet)
• examples/github-actions/README.md — point at tools/loop-action and the refactored workflow examples
• Optional: one-line mention in root README.md Quick Links if other tools are listed there

Acceptance criteria

• Shows uses: cobusgreyling/loop-engineering/tools/loop-action@… with pattern, command, level, sandbox
• Notes week-one report-only / no auto-merge
• Links tools/loop-action/README.md and docs/safety.md
• Mentions that unquoted multi-arg command values are fragile (prefer a single script path)

Estimated time: ~30 minutes

Comment "I'll take this" to get assigned.