feat(webhooks): inspect inbound event payloads

[phucnguyen1707]

Summary

• add a collapsed payload inspector and copy action to recent inbound domain events
• pretty-print valid JSON while preserving number literals, escaped strings, and duplicate keys
• fall back to the original payload for non-JSON, excessively deep, or over-expanded content

Tests

• node --test tests/webhook-payload.test.mjs — 5 passed
• bun test tests/webhook-payload.test.mjs — 5 passed
• npx tsc --noEmit
• npm run build