fix: resolve GITHUB_OUTPUT invalid format when no source files changed

[vigri]

Problem
When no source files changed, grep -c exits with code 1, triggering || echo 0. The trailing newline from echo breaks the $GITHUB_OUTPUT format:

Fix
Replace grep -c || echo 0 with an explicit empty-string check and use printf for clean key=value\n output.

[vigri]

The commit history got a bit messy — sorry about that. I've merged #124 into my fork. @pablogventura let me know if you'd prefer a clean PR instead.

[pablogventura]

You’re right about the history — thanks for flagging it.

If you can redo the branch with a clean history, that would be wonderful and much easier for everyone to review and bisect later.

Thank you again for taking care of it (and for the Node 24 / Actions work alongside this fix).

Kind regards

[vigri]

If you can redo the branch with a clean history

👍