feat: embed Markdown User Guide and AGENTS.md in agent-facing distributions

[osvaldomcc]

Description

• Add a job step to the framework distribution workflow that builds the User Guide as Markdown with sphinx-markdown-builder and embeds it into system/Docs, so coding agents get version-matched documentation alongside the distributed framework.
• Ship �dmin/framework/AGENTS.md to the appstarter repository root on release, pointing agents to the embedded docs.

No framework runtime code is touched; changes are limited to GitHub Actions workflow, the deploy script, and Sphinx build requirements.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication) — no PHP code changed
• Unit testing, with >80% coverage — no PHP code changed; covered by the workflow's est -f ./source/system/Docs/index.md verification step
• User guide updated — no public API/behavior change; CI and release tooling only
• Conforms to style guide

[michalsn]

Thanks for the PR. I don't see a clear benefit to shipping the entire User Guide with every framework installation. Could you clarify:

• How much does this increase the package and download size?
• Why convert to Markdown instead of distributing the existing RST sources?
• What concrete problem does this solve for coding agents?

My take is that AGENTS.md shouldn't be included in every appstarter project. Application owners should decide which instructions apply to agents working on their projects.