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.Application/Auth/Capabilities.cs

@@ -2,7 +2,7 @@ namespace MoShiro.Backend.Application;
 
 /// <summary>
 /// 能力（capability）：一项具体的权限。端点声明自己需要哪一项，<see cref="Principal.Has"/> 是唯一的判断入口，
-/// 会话、API key 都走它。设计见 docs/access.md 第 2 节。
+/// 会话、API key 都走它。设计见 docs/security/access.md 第 3 节。
 /// </summary>
 public static class Capability
 {
@@ -38,7 +38,7 @@ public static class Capability
     public const string EventsRead = "events.read";
     public const string OpsMetrics = "ops.metrics";
 
-    // 预留：外部 webhook 回调和数据拉取（docs/access.md 5.4），目录里先存在，实现放后面
+    // 预留：外部 webhook 回调和数据拉取（docs/security/access.md 6.3），目录里先存在，实现放后面
     public const string DataExport = "data.export";
     public const string WebhooksRead = "webhooks.read";
     public const string WebhooksManage = "webhooks.manage";