docs: reorganize into design, security, api, ops and dev; drop stale designs; refresh the diagrams [CI]

- Group docs by category with an index (docs/README.md); fix every link,
  code comment and the protocol conformance test that read docs/protocol.md.
- access.md and security.md rewritten to what is implemented: removed the
  unadopted member-proof chain, roles and recovery key that do not exist,
  the old implementation order and the budgets; gaps now carry a status.
- enrollment, deployment, api: the install flow is the static, hash-checked
  script with environment variables; no default admin.
- README and architecture: new topology and update-flow diagrams (operator
  passkey, CI signing, registry feed, auth and trust modules).

backend/tests/MoShiro.Backend.Tests/TrustTests.cs

@@ -15,7 +15,7 @@ namespace MoShiro.Backend.Tests;
 
 /// <summary>
 /// 信任根：操作员（passkey）签操作员集合；安装命令里带着创世指纹和属主（都是公开值），节点注册时验证面板的集合并固定在本地。
-/// 设计见 docs/access.md 第 7 节。
+/// 设计见 docs/security/access.md 第 8 节。
 /// </summary>
 [Collection("probe-e2e")]
 public sealed class TrustTests