docs(security): add IAM architecture and end-to-end flow spec for AD/CD/VD LLM Agent defense

[Copilot]

This PR extends the existing layered-defense writeup with implementation-oriented IAM design for in-vehicle 3-domain (AD/CD/VD) LLM Agent scenarios. It adds concrete identity/auth/credential architecture, cross-domain trust/delegation flows, and operational failure/deployment playbooks.

• IAM architecture spec (iam_auth_architecture.md)

  • Adds a full IAM design from task classification through claims model, 4-layer TTL (SVID / Task / Session / Lease), KMSS API integration, lease semantics, delegation chain constraints, and fault matrix.
  • Adds credential lifecycle details: 4-level key hierarchy (K0–K3), OTA trust bundle handling, CRL push/pull strategy, wrapped secret model, and recovery behavior.
  • Adds system-level architecture views (3-domain × 3-module matrix, TEE layering, federation dataflow) and per-module invariants/failure modes for Identity/Auth/Credential.

• Detailed execution/process spec (detailed_architecture.md)

  • Adds operationally detailed design: startup sequencing (cold/hot), internal state machines, and key dependency ordering.
  • Adds 7 key sequence scenarios (same-domain check, cross-domain delegation, lease tightening, emergency revocation propagation, OTA bundle update, KMSS failover, overlap verification).
  • Adds 6 failure drills and a docker-compose demo blueprint (topology, network isolation, persistence, ports, SoftHSM2 vs production TEE boundaries).

• Navigation integration (.vitepress/config.mjs)

  • Adds two sidebar entries under LLM Agent 防御 so the new IAM and detailed architecture docs are first-class and discoverable.

{
  text: 'LLM Agent 防御',
  collapsed: true,
  items: [
    { text: '分层防御方案（IAM + 规则 + Content Guard + NSFA + 沙箱）', link: '/security/llm_agent_defense/layered_defense' },
    { text: 'IAM 认证架构（AD/CD/VD）', link: '/security/llm_agent_defense/iam_auth_architecture' },
    { text: '详细架构（流程 / 状态机 / 演练 / Demo）', link: '/security/llm_agent_defense/detailed_architecture' }
  ]
}