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/ProtocolDeclarationTests.cs

@@ -39,7 +39,7 @@ public sealed class ProtocolDeclarationTests
     public void EveryDeclaredMethod_IsDocumented()
     {
         string root = FindRoot();
-        string docs = File.ReadAllText(Path.Combine(root, "docs", "protocol.md")) + File.ReadAllText(Path.Combine(root, "backend", "fleet", "README.md"));
+        string docs = File.ReadAllText(Path.Combine(root, "docs", "design", "protocol.md")) + File.ReadAllText(Path.Combine(root, "backend", "fleet", "README.md"));
         string[] missing = [.. s_table.Methods.Select(m => m.Name).Distinct().Where(n => !docs.Contains($"`{n}`", StringComparison.Ordinal))];
         Assert.Empty(missing);
     }
@@ -84,7 +84,7 @@ public sealed class ProtocolDeclarationTests
     private static string FindRoot()
     {
         string? dir = AppContext.BaseDirectory;
-        while (dir is not null && !File.Exists(Path.Combine(dir, "docs", "protocol.md")))
+        while (dir is not null && !File.Exists(Path.Combine(dir, "docs", "design", "protocol.md")))
         {
             dir = Path.GetDirectoryName(dir);
         }