feat: add steel section property calculator web app

[bearlove163]

Motivation

• Replace the previous demo page with a compact web tool for computing steel section properties to support quick engineering checks.
• Provide built-in Eurocode and AISC material libraries plus the ability to use custom material values for flexibility.
• Support common section families and presets so users can pick standard profiles or enter custom dimensions and immediately see results.

Description

• Replaced the old Tetris page with a new UI in index.html that includes inputs for material standard/grade, custom material toggle, section type selector, section library, parameter fields, results panels and a real-time SVG preview.
• Implemented material databases and section presets in script.js with MATERIAL_DB and SECTION_LIBRARY, parameter configuration in PARAM_CONFIG, and UI bindings to populate and sync selects/inputs.
• Added section property calculations for rectangle, I-beam and circular pipe types computing A, Ix, Iy, Wx, and Wy with basic geometric validation and error messaging.
• Revamped styling in style.css into a responsive two-column engineering panel with cards for inputs/results and a live #sectionSvg drawing that updates as parameters change.

Testing

• Ran a syntax check with node --check script.js, which completed successfully.

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Codex Task