fix(chat): render all inline media parts

[DorianChn]

Summary

• Preserve all inline data parts when building chat UI events, while keeping the existing single-part field compatible.
• Render every media part and cover multi-part rendering and streamed partial updates with regression tests.

Why

• In the multiple-image case reported in Web UI fails to render non-text parts #414, the UI event model retained only the last inlineData part, so earlier media from the same response was lost.

Validation

• npm test -- --watch=false --browsers=ChromeHeadlessCI (763 passed; 37 skipped)
• npm run build (passed)

Addresses #414.