docs: add 6 comprehensive governance tutorials (#187)

* docs: add tutorial 02 — trust and identity system

Covers agent DIDs (Ed25519), trust scoring (0-1000 scale with ring tiers),
credential lifecycle (15-min TTL, rotation, revocation), trust-based access
control with YAML policies, and multi-agent trust mesh handshake protocol.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* docs: add 5 governance tutorials (policy, integrations, audit, SRE, sandboxing)

- 01-policy-engine.md: YAML syntax, operators, conflict resolution, middleware
- 03-framework-integrations.md: OpenAI, LangChain, CrewAI, Anthropic wrapping
- 04-audit-and-compliance.md: Merkle audit logs, OWASP ASI compliance CLI
- 05-agent-reliability.md: Rogue detection, circuit breakers, SLOs, chaos testing
- 06-execution-sandboxing.md: 4-ring model, capability guards, saga orchestration

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: imran-siddique