docs: clarify implemented agent capabilities and maturity

[CodeWithJuber]

Summary

• surface the implemented Python/FastAPI agent loop, function calling, tools, memory, delegation, APIs and guardrails
• link recruiter-facing claims to source and dated CI evidence
• separate implemented, partial and absent capabilities, including Chroma, HITL, councils, Azure and named frameworks
• preserve setup, architecture, API and contributor documentation

Evidence boundary

Mizan remains labelled a public beta research prototype; no enterprise production use is claimed.

Validation

• 50/50 relative links and 7/7 anchors resolved
• 26 API routes, documented Make targets, CLI commands and Compose settings checked against source
• Markdown, fences, tables and whitespace checks passed