Replace the dynamic error message in the webhook JSON parsing error
path with a static message. Previously, the raw JsonRejection error
from axum/serde was interpolated into the HTTP response, potentially
exposing internal parsing details to unauthenticated callers.
The detailed error is now logged server-side via tracing::warn for
debugging, while the client receives a generic "Invalid JSON body"
message.
Closes#356
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
e6ad48df48