Make PHP_CodeSniffer a blocking check (phpcbf baseline cleanup) #417

Summary

PHP_CodeSniffer (advisory) in tests.yml reports violations but never fails, because the codebase has a baseline of 422 errors (all auto-fixable by phpcbf) and 290 warnings in 139 files. Clean up the baseline and make the check blocking so it can be added to the required checks.

Scope

• Run phpcbf over the files configured in phpcs.xml; formatting only, no behaviour change.
• Keep warnings (line length, _-prefixed ItemController hooks) non-blocking.
• CI job PHP_CodeSniffer: on pull requests check changed files and fail on errors; on main check the whole repository and fail on errors.
• Add the reformatting commit to .git-blame-ignore-revs.

Acceptance criteria

• vendor/bin/phpcs reports 0 errors on main.
• The PHPUnit suite is unchanged (same tests, all passing).
• The job fails on a PR that introduces a PHPCS error and passes on warnings only.