docs: add chart props reference and Recharts children anti-pattern

[keugenek]

Summary

AppKit charts are ECharts-based and do not accept Recharts children components. This was causing TypeScript build errors when LLMs generated code mixing AppKit chart components with Recharts primitives like <Bar>, <XAxis>, <CartesianGrid>, etc.

Problem

LLMs were generating code like:

<BarChart queryKey="data" parameters={{}}>
  <CartesianGrid strokeDasharray="3 3" />
  <XAxis dataKey="region" />
  <Bar dataKey="revenue" fill="#40d1f5" />
</BarChart>

This causes TypeScript errors because AppKit's BarChart doesn't accept children - it's a self-contained ECharts component.

Solution

Added explicit documentation to llms.txt:

• Chart props reference showing correct usage (xKey, yKey, colors, stacked, etc.)
• Critical anti-pattern warning about Recharts children not being supported
• Updated LLM checklist with chart-specific guidance

Changes

• Add chart props reference with correct usage examples
• Add explicit anti-pattern warning about Recharts children
• Update LLM checklist with chart-specific items

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