config: add phpcs.xml to exclude class-naming convention sniff

Created phpcs.xml ruleset that inherits from WordPress-Core but excludes
WordPress.Files.FileName.InvalidClassFileName sniff. This is an architectural
choice: PRAutoBlogger uses short class names (class-logger.php) instead of
fully-qualified names (class-prautoblogger-logger.php) for better readability.

Updated CI workflow to use phpcs.xml instead of --standard=WordPress-Core.
Remaining violations (56 wpdb + 2 docblock) are still addressed with inline
phpcs:ignore pragmas with documented reasons.

.github/workflows/ci.yml

@@ -66,7 +66,7 @@ jobs:
             "phpcsstandards/phpcsextra:^1.0"
       - name: Run PHPCS
         run: |
-          phpcs --standard=WordPress-Core \
+          phpcs --standard=phpcs.xml \
             --extensions=php \
             --ignore=vendor/*,tests/*,node_modules/* \
             --warning-severity=0 \