docs: update README for latest platform capabilities

[Kristariss]

What changed

• Reframe InsideGov as an organization-centered multi-agent policy laboratory.
• Document the five problem-first public experiences and four macro outcomes.
• Explain the current cognition, organization-process, capability, rule-engine, audit, and persistence architecture.
• Add the latest evidence-gated due diligence, imitation/exit/rescue, public LLM, and durable-job capabilities.
• Correct setup guidance: public experiences require DeepSeek while deterministic research remains available without a key.
• Refresh commands, repository structure, verification, research boundaries, and security notes.

Why

The previous README still described the homepage primarily as an offline deterministic five-minute demo and did not cover the latest public experience and organization-autonomy work merged after v0.6.0.

Validation

• git diff --check
• all relative README links resolve locally
• documented InsideGov CLI subcommands exist
• README secret-pattern scan passed

Documentation-only change; no runtime behavior is modified.