Add Generative UI Data Chat reference app

[vishxrad]

Summary

Adds apps/generative-ui-data-chat, a Next.js + OpenUI reference app for Oracle AI Database 26ai that answers business-data questions as typed UI components instead of markdown.

The app demonstrates SQL, vector, and hybrid retrieval over a seeded revenue/accounts/users/contracts dataset, then renders the response as charts, KPI cards, tables, source cards, mixed insight views, follow-up prompts, and an Oracle execution trace.

What changed

• Added a standalone Next.js App Router app with TypeScript, Tailwind CSS, OpenUI, Recharts, Zod, lucide icons, and the Oracle Node.js thin driver.
• Added /api/chat, a Node runtime API route that streams progress events and returns a validated DataChatResponse.
• Added Oracle Database Free/26ai Docker setup and seed scripts.
• Added seeded data for revenue, accounts, active users, contracts, and contract chunks.
• Added SQL, vector, and hybrid retrieval paths.
• Added categorized sample prompts and follow-up CTA buttons.
• Added README documentation, demo video link, environment variables, architecture notes, and limitations.
• Updated root README.md and apps/README.md.

Testing

• npm run lint
• npm run test
• npm run build
• Manual browser smoke test on localhost:3001
• Verified demo prompt: Revenue trend over the last 12 months
• Verified /api/chat returns 200 and renders Oracle SQL trace

closes #132

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