Add community module documentation authoring guide

[ihsraham]

Summary

• add a complete contributor guide for authoring consistent WDK community-module documentation
• add a reusable workspace skill with installation and usage guidance
• add validation for artifact structure, Markdown integrity, isolated authoring output, and API-reference readiness

Information architecture

The contributor artifacts live outside content/docs, so this change adds no rendered documentation routes and requires no sidebar update.

Validation

• artifact validator and self-tests pass
• all 34 embedded shell examples pass syntax checking
• staged diff passes whitespace checks