Fix 3-col calculator labelling and add lint

hdyc-svelte/scripts/lint-3col.mjs

@@ -0,0 +1,36 @@
+#!/usr/bin/env node
+import { readFileSync } from 'fs';
+import path from 'path';
+
+const file = path.resolve('src/lib/data/calculators.ts');
+const text = readFileSync(file, 'utf8');
+const start = text.indexOf('[');
+const end = text.indexOf('];', start);
+if (start === -1 || end === -1) {
+  console.error('Unable to locate calculators array in calculators.ts');
+  process.exit(1);
+}
+let arr = text.slice(start, end + 1).trim();
+arr = arr.replace(/,\s*\]$/, ']');
+let calculators;
+try {
+  calculators = JSON.parse(arr);
+} catch (err) {
+  console.error('Failed to parse calculators.ts as JSON:', err.message);
+  process.exit(1);
+}
+
+const offenders = calculators.filter(c =>
+  ['3col', '3col-mul'].includes(c.type) &&
+  c.name.toLowerCase().includes(' to ') &&
+  (!c.labels?.in3 || c.labels.in3.toLowerCase() === 'result')
+);
+
+if (offenders.length) {
+  console.error(`3-col calculators with vague or missing output labels: ${offenders.length}`);
+  offenders.slice(0, 20).forEach(c => console.error(`- ${c.slug}`));
+  if (offenders.length > 20) console.error(`…and ${offenders.length - 20} more`);
+  process.exit(1);
+}
+
+console.log('3-col label lint passed.');