feat(server): add persistence types and ClientRecord structure

- Add ClientRecord, ClientSession, ServerRegistry interfaces
- Add serialization helpers for persistent storage
- Add state check functions (isPairable, canAuthenticate, etc.)
- Export persistence types from plugin index.ts

plugin/index.ts

@@ -1,5 +1,24 @@
 export { validateYonexusServerConfig, YonexusServerConfigError } from "./core/config.js";
 export type { YonexusServerConfig } from "./core/config.js";
+export {
+  createClientRecord,
+  serializeClientRecord,
+  deserializeClientRecord,
+  isPairable,
+  hasPendingPairing,
+  isPairingExpired,
+  canAuthenticate,
+  type PairingStatus,
+  type ClientLivenessStatus,
+  type PairingNotifyStatus,
+  type NonceEntry,
+  type HandshakeAttemptEntry,
+  type ClientRecord,
+  type ClientSession,
+  type ServerRegistry,
+  type SerializedClientRecord,
+  type ServerPersistenceData
+} from "./core/persistence.js";
 
 export interface YonexusServerPluginManifest {
   readonly name: "Yonexus.Server";