Webhook-to-SSE gateway with hierarchical topic routing and signature verification

Make LookupVerification inherit from parent paths master

LookupSubscribeSecret already walks up the path hierarchy, but LookupVerification required an exact match. If you configured verification at `github.com`, a POST to `github.com/org/repo` would skip signature checking entirely. Now it uses the same walk-up loop. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>