docs: add GAIA to ADOPTERS.md

[aryanranderiya]

Adds GAIA to the OpenUI adopters list, per Visharad Kashyap's request.

Field	Value
Organization / Project	GAIA
Contact	Aryan Randeriya
Use of OpenUI	GAIA is a proactive personal AI assistant that uses OpenUI Lang to let its backend LLM emit rich, interactive React components inline in chat responses — rendering cards, lists, and other generative UI directly in the conversation instead of plain text.

Single-row addition to the table in ADOPTERS.md; no other changes.