fix: address PR #10 CodeRabbit review feedback (issue #45) (#51)

* fix: address PR #10 CodeRabbit review feedback

- Fix SC2115 shellcheck warning in build.sh (use ${var:?} for safe rm -rf)
- Fix SC2164 shellcheck warning in build.sh (cd build || exit 1)
- Standardise bullet points from hyphens to asterisks in .wiki/Contributing.md
- Refine verb formality in readme.txt, README.md, .wiki/Contributing.md, .wiki/Coding-Standards.md
- Clarify PHPDoc wording in .wiki/Coding-Standards.md
- Add clarifying comment to phpcs-simple.xml arg value

* fix: re-enable PHPUnit test step in tests.yml

Tests were commented out in PR #10. PHPUnit test files exist in
tests/phpunit/ and phpunit.xml is configured. Re-enabling the step
so tests actually run in CI.

Closes #45

* fix: remove redundant composer require steps in code-quality workflow

szepeviktor/phpstan-wordpress, wp-coding-standards/wpcs, and
dealerdirect/phpcodesniffer-composer-installer are already declared in
composer.json require-dev. The extra 'composer require' steps after
'composer install' caused a second packagist.org network hit that timed
out in CI, failing the PHPStan Static Analysis job.

Fixes the Code Quality CI failure on PR #51 (issue #45).

phpcs-simple.xml

@@ -14,7 +14,7 @@
     <exclude-pattern>*/build/*</exclude-pattern>
     <exclude-pattern>*/dist/*</exclude-pattern>
 
-    <!-- Command line arguments -->
+    <!-- Command line arguments: combined short flags (-s shows sniff codes, -p shows progress) -->
     <arg value="sp"/>
     <arg name="extensions" value="php"/>
     <arg name="basepath" value="."/>