fix(core): add additional spec-validator checks for common LLM errors

[nil957]

Summary

Extends validateSpec and autoFixSpec to detect and repair more common AI-generation mistakes.

New Validation Checks

Code	Description
action_in_props	Legacy action prop placed inside props
actionParams_in_props	Legacy actionParams placed inside props
children_in_props	Children array placed inside props instead of element level
state_in_props	State object placed inside element props

Example: action_in_props

// ❌ Wrong (LLM-generated)
{
  "type": "Button",
  "props": { "label": "Submit", "action": "save", "actionParams": { "id": 1 } }
}

// ✅ Correct
{
  "type": "Button",
  "props": { "label": "Submit" },
  "on": { "press": { "action": "save", "params": { "id": 1 } } }
}

Example: children_in_props

// ❌ Wrong
{
  "type": "Stack",
  "props": { "children": ["a", "b"] }
}

// ✅ Correct
{
  "type": "Stack",
  "props": {},
  "children": ["a", "b"]
}

Auto-Fix Enhancements

autoFixSpec now automatically repairs:

1. children in props → moves to element level
2. Legacy action/actionParams → converts to on.press binding

Motivation

LLMs frequently make these mistakes because:

• action/actionParams was a pattern from earlier versions
• children feels like a natural prop name
• React's props.children pattern is well-known

Better detection + auto-fix improves the success rate of AI-generated specs.

Checklist

• Tests added for new validation codes
• Tests added for auto-fix cases
• No breaking changes
• Error messages include guidance on correct structure

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