axios was required by src/utils/message.js and src/utils/webhook.js but was
never declared in package.json, so `npm install` never fetched it and the app
crashed on startup with MODULE_NOT_FOUND.
Switch both webhook POST calls to Node's built-in fetch (available since
Node 18; running on 22.12), removing the missing dependency entirely.
Behavior is preserved: JSON body with Content-Type header, and an explicit
response.ok check to keep axios's throw-on-non-2xx semantics. message.js now
returns parsed JSON (or text fallback) in place of axios's response.data.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
