Add testing and coding agent guides to each template's docs #96

Engineers working in a generated solution have no page on where a test goes or how to clear the 95% coverage bar before CI does, and the agent instructions that ship with every solution (AGENTS.md, Jacques and the skills) only appear in the project structure.

Phase 1: The guides

• guides/test-your-changes.mdx per template: the four test projects, what each kind of code needs, and the coverage command CI runs
• guides/work-with-a-coding-agent.mdx per template: what ships, getting started, making it yours, what the agent won't do
• One opening line on each How it's built page saying it describes the template's own pipeline, pointing to Set up CI

Checks: the site builds. Site PR LeanMeanCleanApps/leanmeancleanapps.github.io#29.