fix(ci): pin PHPCS to ^3.13 for WPCS compatibility

PHPCS 4.0.1 was installed first via sequential composer require,
locking the version before WPCS could constrain it. WPCS 3.x
requires PHPCS ^3.x. Fix: install all packages in one command
with --with-all-dependencies and pin PHPCS to ^3.13.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -30,9 +30,10 @@ jobs:
 
       - name: Install PHPCS + WordPress standards
         run: |
-          composer global require "squizlabs/php_codesniffer=*"
-          composer global require "wp-coding-standards/wpcs=*"
-          composer global require "phpcsstandards/phpcsutils=*"
+          composer global require --with-all-dependencies \
+            "squizlabs/php_codesniffer=^3.13" \
+            "wp-coding-standards/wpcs=^3.0" \
+            "phpcsstandards/phpcsutils=^1.0"
           phpcs --config-set installed_paths $(composer global config home)/vendor/wp-coding-standards/wpcs
 
       - name: Run PHPCS