feat: port session 11 — Accounts & Directory JWT Store

- Account: full Account class (200 features) with subject mappings,
  connection counting, export/import checks, expiration timers
- DirJwtStore: directory-based JWT storage with sharding and expiry
- AccountResolver: IAccountResolver, MemoryAccountResolver,
  UrlAccountResolver, DirAccountResolver, CacheDirAccountResolver
- AccountTypes: all supporting types (AccountLimits, SConns, ExportMap,
  ImportMap, ServiceExport, StreamExport, ServiceLatency, etc.)
- 34 unit tests (599 total), 234 features complete (IDs 150-349, 793-826)

dotnet/src/ZB.MOM.NatsNet.Server/NatsServer.Init.cs

@@ -1044,7 +1044,7 @@ public sealed partial class NatsServer
             {
                 // Validate JWT format (stub — session 06 has JWT decoder).
                 // jwt.DecodeAccountClaims(v) — skip here, checked again in CheckResolvePreloads.
-                ar.Store(k, v);
+                ar.StoreAsync(k, v).GetAwaiter().GetResult();
             }
         }
         return null;