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

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="."/>