feat: add CSS Box Shadow Generator tool

Summary

Add a box-shadow.html visual builder for the CSS box-shadow property — slider controls, multi-layer support, live card preview, and copy-ready CSS output.

Motivation

CSS box-shadow builders are consistently popular among front-end developers who want to iterate visually rather than guess numeric values. It extends the existing design-tool cluster (Gradients, Blob, Waves) into practical CSS generation and requires zero external dependencies.

Proposed UX

• Live preview card: a resizable box in the center showing the shadow in real time against light and dark backgrounds (toggle)
• Per-layer controls (panel on the side):
  • X offset, Y offset, Blur radius, Spread radius — numeric inputs + range sliders
  • Color swatch (.color-btn) with opacity slider
  • inset toggle
  • Duplicate / delete layer buttons
• Layer list: add up to 8 shadow layers; drag to reorder; active layer highlighted
• Output panel:
  • Generated box-shadow: … CSS (multi-layer comma-joined)
  • Tailwind v3/v4 shadow-[…] arbitrary-value string
  • One-click copy for both
• Preset gallery: 6–8 named shadow recipes (e.g. Soft, Elevated, Crisp, Inset, Neon glow) that load a layer config

Implementation notes

• Category: Ornaments
• Slug: box-shadow
• Icon: 🌑
• No npm dependencies — all CSS value assembly is inline string interpolation
• All logic inline in <script>
• Use .angle-dial from the design system for the optional light-direction knob if added
• 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 src/_tool-template.html and inspect the existing design-tool cluster for the expected structure and interactions. Add the tool entry to tools.json, then run bun run generate:sections, bun run generate:index, and bun run generate:favicon. Done means the builder supports the listed layer controls, previews and presets, produces copyable CSS and Tailwind output, and has the requested live interactions.