feat: add console.md

[magnus-madsen]

Summary

• Extract the Console section from library-effects.md into its own console.md page
• Add expanded documentation covering the Console effect, Sys.Console module, basic I/O, confirmed input, and validated input
• Add Console entry to SUMMARY.md

Test plan

• Verify the book builds successfully with mdbook build
• Check that the Console page renders correctly and all code examples are properly formatted

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