docs: Reposition the README around the self-operating server

[nfebe]

Brings the agent repo's README in line with the positioning shipped on the site (flatrun/website#12): hosting OS, platform API, agent engine, with governance framing for agent actions.

[sourceant]

Code Review Summary

The PR successfully repositions the project's README from a standard 'hosting control plane' to a 'self-operating platform'. It introduces key concepts such as the 'hosting OS', 'agent engine', and user-defined 'governance', aligning the repository with the project's broader strategic direction.

🚀 Key Improvements

• Updated project description to focus on the 'self-operating' and 'hosting OS' metaphors.
• Added a dedicated section for 'Agent-native' capabilities, including Markdown-based agent definitions.
• Introduced references to the MCP (Model Context Protocol) for external agent interoperability.
• Clarified the role of governance in AI-driven operations.

💡 Minor Suggestions

• Capitalize technical proper nouns like 'Markdown' for professional consistency.
• Check pluralization consistency ('GitHub Actions' vs 'GitHub Action').

[sourceant]

Review complete. No specific code suggestions were generated. See the overview comment for a summary.