Scope Pint guideline to PHP file changes only

[pushpak1300]

Agents were running Pint unconditionally — even for documentation, config, or frontend-only changes — wasting tokens and adding unnecessary latency to every transaction.

Fixes #586

Approach

• Add an "only if PHP files were modified" condition to the Pint run instruction, giving agents a clear and cheap signal to skip formatting when it isn't needed