Recover legacy notification transport backoff

[ael-dev3]

Summary

• recognize the exact legacy broad-transport diagnostics written by the affected Cloudflare deployment
• let an authenticated operator bring only that generation’s persisted fifth retry forward after the 30-second Farcaster floor
• preserve the stable notification ID, current admission resolver check, stored backoff lifetime, and six-attempt ceiling
• keep current classified failures on their normal backoff

No SpacetimeDB schema, frontend, game state, secret, or notification token changes are included.

Verification

• pnpm --dir services/auth-bridge run check
  • 310 unit tests
  • 12 Workerd tests
  • both TypeScript checks
• git diff --check
• exact CI gitleaks history scan: no leaks