Export calculation engine as standalone npm package

[Copilot]

The Next.js application's calculation engine can now be consumed as an npm package by external applications.

Changes

Library Export (lib/index.ts)

• Exports formula access (getFormula, formulaData, evaluateFormulaOutputs)
• Exports medical utilities (BSA_DuBois, GetZScore, erf, etc.)
• Exports all TypeScript types (Formula, FormulaData, FormulaInput/Output)

Build Pipeline

• Added tsconfig.lib.json targeting CommonJS for Node.js compatibility
• Integrated tsc-alias to resolve @/* path mappings at build time
• Build script: npm run build:lib

Package Configuration

• Removed private: true, added main and types fields
• files whitelist: dist/, src/formulas/
• prepublishOnly hook ensures build before publish

Type Safety

• Fixed CalculationFormula and HtmlFormula to include base Formula fields (name, info, metadata, locales)

Usage

import { getFormula, evaluateFormulaOutputs } from 'med';

const formula = getFormula('bmi_adult');
const results = evaluateFormulaOutputs(formula, {
  height: 170,
  weight: 70
});
// { BMI: 24.2, who_diag: "normal", jasso_diag: "普通体重" }

Core dependencies: expr-eval, zod. Next.js/React dependencies included but not required for calculation functionality.

Original prompt

The current code is working perfectly fine. It functions flawlessly as a Next.js application, and the API features are also operational.
However, I also thought it would be more convenient if other applications could utilize this calculation feature as well.
Make calculation feature available for use by installing it via npm from another application.

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