refactor: migrate to ES modules

package.json type=module, tsconfig module/moduleResolution=NodeNext,
target es2022, explicit .js on all relative imports. Center: jsonwebtoken
& bcryptjs switched to default imports (ESM/CJS interop). Verified:
builds, boots, full auth + plugin round-trip work under ESM.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/events/events.service.ts

@@ -1,6 +1,6 @@
 import { Injectable, Logger } from '@nestjs/common';
 import { createHmac, randomUUID } from 'crypto';
-import { FabricEventEnvelope } from './event-envelope';
+import { FabricEventEnvelope } from './event-envelope.js';
 
 type RetryTask = {
   envelope: FabricEventEnvelope;