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/src/MoShiro.Backend.Api/Admin/TrustEndpoints.cs

@@ -8,7 +8,7 @@ using MoShiro.Protocol;
 namespace MoShiro.Backend.Api;
 
 /// <summary>
-/// 信任根（docs/access.md 第 7 节）：操作员集合由 passkey 签名，节点从安装命令里固定的创世指纹出发验证它；
+/// 信任根（docs/security/access.md 第 8 节）：操作员集合由 passkey 签名，节点从安装命令里固定的创世指纹出发验证它；
 /// 带操作员委托的加入码也在这里创建——委托是 passkey 对「这个码」签的，面板自己签不出来。
 /// </summary>
 public static class TrustEndpoints