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/messaging/pagination.util.spec.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from 'vitest';
-import { clampLimit, computeNextExpectedSeq } from './pagination.util';
+import { clampLimit, computeNextExpectedSeq } from './pagination.util.js';
 
 describe('pagination utils', () => {
   it('clamps limit safely', () => {