When renderUrlPdf() sets up request interception for SSRF DNS pinning,
the interceptor and event listener were never cleaned up in recyclePage().
This could cause subsequent HTML-to-PDF conversions on the same pooled
page to have external resources blocked by the stale interceptor.
- Export recyclePage for testability
- Add removeAllListeners('request') + setRequestInterception(false)
- Add browser-recycle.test.ts with TDD (red→green verified)
Tests: 443 passing (was 442)
