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/CapabilityTests.cs

@@ -8,7 +8,7 @@ using MoShiro.Backend.Application;
 
 namespace MoShiro.Backend.Tests;
 
-/// <summary>能力模型（docs/access.md 第 2 节）：每个管理端点声明能力；密钥只能拿到自己拥有能力的子集；写蕴含读。</summary>
+/// <summary>能力模型（docs/security/access.md 第 3 节）：每个管理端点声明能力；密钥只能拿到自己拥有能力的子集；写蕴含读。</summary>
 [Collection("probe-e2e")]
 public sealed class CapabilityTests
 {