* fix(webui): show helpful errors for incompatible configurations
- show error when Gateway.NoFetch=true and WebUI is not available locally
- show error when Gateway.DeserializedResponses=false (incompatible)
- add tests for both error scenarios
* chore(webui): update to v4.9.0
https://github.com/ipfs/ipfs-webui/releases/tag/v4.9.0
* docs: add WebUI v4.9.0 update to v0.38 changelog
- highlight new diagnostics screen for troubleshooting
- include screenshots of key features in table format
- add local access URL for WebUI
- update TOC with new sections
