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/InstallScripts.cs

@@ -6,7 +6,7 @@ namespace MoShiro.Backend.Api;
 
 /// <summary>
 /// 一行安装脚本：<c>packaging/install/</c> 下的 <c>install.sh</c> 和 <c>install.ps1</c> 作为嵌入资源打进 Backend，<b>原样返回，不替换任何值</b>。
-/// 静态，所以它的 SHA-256 在一个版本内固定：CI 构建时算出来写进签名的发布清单，面板给的命令先核对哈希再执行（docs/access.md 第 15 节）。
+/// 静态，所以它的 SHA-256 在一个版本内固定：CI 构建时算出来写进签名的发布清单，面板给的命令先核对哈希再执行（docs/security/access.md 第 10 节）。
 /// 角色、面板地址、代码都走命令里的环境变量。
 /// </summary>
 public static class InstallScripts