docs: document tool error handling with ToolException

[tomivirkki]

Summary

• Documents the ToolException contract introduced in feat: add ToolException for LLM-safe tool errors flow-components#9957: only its message is relayed verbatim to the LLM, while any other exception from tool code is logged and replaced with a generic error.
• Corrects the AI-Powered Grid page, which claimed failed query probe errors are returned to the model — relaying is opt-in, requiring the DatabaseProvider implementation to throw ToolException. Adds the matching validation section for AI-Powered Chart.
• Clarifies that vendor-annotated @Tool objects are out of this contract's scope, since LangChain4j and Spring AI apply their own error handling.

[github-actions]

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URL: https://docs-preview-pr-5900.fly.dev

Changed pages

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

• flow/ai-support/ai-powered-chart — modified, +7/-0 lines
• flow/ai-support/ai-powered-grid — modified, +3/-1 lines, 1 removal marker(s)
• flow/ai-support/controllers — modified, +35/-2 lines, 2 removal marker(s)
• flow/ai-support/tool-calling — modified, +4/-0 lines

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