* feat(mcp): add XML validation and auto-fix to MCP server
- Add xml-validation.ts with validateAndFixXml function
- Integrate validation into display_diagram tool (fails if unfixable)
- Integrate validation into edit_diagram tool (auto-fix each operation)
- Fix bug: typo fixes now run before foreign tag removal
- Fix bug: use before/after comparison instead of regex .test()
* style: auto-format with Biome
* chore(mcp): bump version to 0.1.3
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