Post-1.3: stats detail drawer renders duplicate and noisy event payloads

Manual 1.3 testing: stats detail drawers showed the same event twice: formatted JSON at the top, then a second key/value dump below. Some panels also showed many null fields and dense body metadata that crowded out the useful payload.

Expected:
- Do not show the same information twice.
- Hide null/empty fields unless explicitly requested.
- Render request/response bodies with MIME-aware formatting and syntax coloring.
- Keep raw JSON available as a deliberate debug view, not as duplicated default content.

Post-1.3 UI cleanup.

Start by reproducing the issue in the stats detail drawers during manual 1.3 testing and trace the current event-payload rendering path. Verify the default view removes duplicated information and null or empty fields, formats request and response bodies by MIME type with syntax coloring, and keeps raw JSON behind an explicit debug view.

Written by the indexing model from the issue text.