Public endpoint (no auth token) protected by per-routine webhook secrets
with constant-time comparison via subtle::ConstantTimeEq.
Matches path against routines with Trigger::Webhook, validates
X-Webhook-Secret header, and fires the routine through the message
pipeline. Returns 404/401/200 as appropriate.
2 unit tests for secret comparison and path matching.
Co-Authored-By: Claude Opus 4.6 <[email protected]>