feat: add Barcode Generator tool

Summary

Add a barcode-generator.html tool supporting the most common 1D barcode formats — a natural sibling to the existing QR Code Generator.

Motivation

"barcode generator online" has solid search volume, particularly from e-commerce developers, warehouse operators, and product teams who need quick test barcodes without installing desktop software. The QR Code Generator already owns this UX pattern in the project — the Barcode Generator reuses it and cross-links naturally.

Proposed UX

• Format selector pills: Code 128 · Code 39 · EAN-13 · EAN-8 · UPC-A · UPC-E · ITF-14
• Input field: updates live; shows a validation error for format-specific constraints (EAN-13 requires exactly 12 digits + auto-computed check digit, etc.)
• Live SVG preview of the barcode with human-readable text below
• Options:
  • Show / hide text label below the barcode
  • Bar height (px)
  • Bar width (narrow bar multiplier)
  • Foreground + background color swatches
  • Quiet zone toggle
• Export: SVG download · PNG at 1× / 2× / 4× · Copy PNG to clipboard
• Cross-link to QR Code Generator in the UI ("Need a 2D code instead? →")

Implementation notes

• Category: Generators (next to qr-code-generator.html)
• Slug: barcode-generator
• Icon: 📊
• Library: JsBarcode (MIT, ~30 KB) renders directly to an <svg> element — use a UMD bundle inlined at build time (same pattern as js-yaml in json-to-yaml.html) to avoid the sibling-module overhead for this relatively simple integration
• Follow src/_tool-template.html and run bun run generate:sections, bun run generate:index, bun run generate:favicon after adding to tools.json

Start with qr-code-generator.html and src/_tool-template.html to understand the existing generator UX and single-file integration pattern. Add the barcode-generator entry to tools.json, then run bun run generate:sections, bun run generate:index, and bun run generate:favicon. Done means the listed formats, validation, live SVG preview, options, exports, and QR Code Generator cross-link work as described.