fix: sync shadow tokens with Figma and remove dark elevation utilities

[netchampfaris]

Syncs shadow tokens with the Figma source of truth and removes unused dark elevation utilities.

• Reverse layer order in shadowToCss so CSS paint order matches Figma
• Update light-mode shadow values to match Figma
• Remove unused shadow-dark-* utilities and --dark-elevation-* vars
• Make elevation preview boxes square

🤖 Generated with Claude Code

Docs preview: https://ui.frappe.io/pr-preview/pr-781/

Coverage: 56.52% (+0.01% vs main)

[barista-for-frappe]

Looks good — design-token sync, no public component API touched.

• tailwind/figma-tokens-to-theme.js:322 — reversing layers so CSS paint order matches Figma is a real fix; the regenerated effects.json is consistent (light + dark both reversed, source colors updated to match effect.styles.tokens.json).
• Removing shadow-dark-* / --dark-elevation-* is safe: grep finds zero consumers across the repo, and the comment in colorPalette.js:131 already documents that dark mode uses the light/* values. Pre-v1 beta, so the freeze (P13) doesn't bite.

Minor nit:

• tailwind/generated/effects.json:11 — elevation.dark is still generated but now has no CSS var or utility consuming it. Harmless (it's build output), just dead data now that the dark utilities are gone.