docs: mark built-in AI controllers as commercial features

[tomivirkki]

Summary

• feat!: split AI components into free and pro modules flow-components#9887 splits the AI components into an open-source vaadin-ai-core-flow module and a commercial vaadin-ai-extensions-flow module containing the built-in Grid, Chart, and Form AI controllers
• Adds the commercial banner and section-nav: commercial badge to the AI-Powered Grid/Chart and AI Form Filler pages, and clarifies in the AI Integration overview and Controllers reference which parts require a commercial subscription
• Custom AIController implementations and DatabaseProvider remain free, which the Controllers page now states explicitly

🤖 Generated with Claude Code

[github-actions]

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URL: https://docs-preview-pr-5879.fly.dev

Changed pages

Added content is highlighted in green; removed content is marked in red on each page.

• building-apps/ai — modified, +1/-1 lines, 1 removal marker(s)
• components/charts/ai-powered — modified, +4/-1 lines
• components/form-layout — modified, +1/-1 lines, 1 removal marker(s)
• components/form-layout/ai-powered — modified, +4/-1 lines
• flow/ai-support — modified, +3/-1 lines, 1 removal marker(s)
• flow/ai-support/ai-powered-chart — modified, +4/-0 lines
• flow/ai-support/ai-powered-form — modified, +4/-0 lines
• flow/ai-support/ai-powered-grid — modified, +4/-0 lines
• flow/ai-support/controllers — modified, +5/-0 lines

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