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).

build.sh

@@ -71,7 +71,7 @@ if [ -d "vendor" ]; then
 	cp -R vendor "$BUILD_DIR/"
 fi
 
-# Create ZIP file
+# Create ZIP file.
 echo "Creating ZIP file..."
 cd build || exit 1
 zip -r "../$ZIP_FILE" "$PLUGIN_SLUG" -x "*.DS_Store" -x "*.git*" -x "*.github*"
@@ -87,7 +87,7 @@ if [ -f "$ZIP_FILE" ]; then
 		printf '\nDeploying to local WordPress installation...\n'
 		echo "Deploying to local WordPress installation..."
 
-		# Remove existing plugin directory
+		# Remove existing plugin directory.
 		rm -rf "${WP_LOCAL_PLUGIN_DIR:?}/$PLUGIN_SLUG"
 
 		# Copy files to local WordPress installation