Checkpoint 1: implement native subsystems and begin the gameplay manual

docs/manual/contributing.md

@@ -0,0 +1,20 @@
+# Keep the manual executable
+
+Document user tasks and actual APIs in English. Explain what each argument means,
+which callback it belongs in, and what happens when an object or resource is missing.
+
+Prioritize complete small gameplay examples over isolated declarations. Link examples
+to their source files and include them in build or integration checks. When an API
+changes, update its examples in the same change.
+
+Mark planned capabilities explicitly. Do not describe a prototype image as a running
+editor, a Linux test as Windows validation, or a planned feature as implemented.
+
+Build with strict documentation validation before publishing:
+
+```sh
+.cache/docs-venv/bin/python -m mkdocs build --strict
+```
+
+Generated output goes to `build/manual`; source Markdown and configuration are tracked
+in Git. Research and architecture documents remain separate from this user manual.