LevelChat Webhooks

v0.1.0

Outbound webhook events delivered by `webhooks-svc`. Receivers must dedupe on `X-LC-Webhook-Id` and verify HMAC. Signature is `base64( HMAC-SHA-256(secret, ts + "." + body) )` — see `services/webhooks/internal/delivery/sign.go` for the authoritative wire contract.