feat: add gruvbox theme

[aidankmcalister]

Summary

Adds a new gruvbox theme to Better Hub with one dark variant and one light variant, based on the official Gruvbox palette.

What changed

• Added gruvbox theme definition in apps/web/src/lib/themes/themes.tsx
  • id: "gruvbox"
  • Dark variant using classic Gruvbox dark tones (dark0, warm foreground, orange/yellow/green accents)
  • Light variant using classic Gruvbox light tones (light0, faded accent set)
  • Includes full theme token mapping (--background, --foreground, --card, --link, diff colors, alerts, contribution heatmap colors, etc.)
  • Includes syntax highlighting mappings for both dark and light variants
• Registered gruvbox in apps/web/src/lib/themes/index.ts so it appears in the app theme picker.

Notes

• Kept implementation simple: one theme ID with exactly two variants (dark + light).
• Palette choices were mapped directly from Gruvbox’s original color families (dark/light, bright/faded, neutral accents).

Validation

• Ran typecheck successfully:
  • cd apps/web && bun run typecheck
• Ran formatting check on modified theme files:
  • oxfmt --check apps/web/src/lib/themes/themes.tsx apps/web/src/lib/themes/index.ts

[vercel]

@aidankmcalister is attempting to deploy a commit to the better-auth Team on Vercel.

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[ping-maxwell]

Hey I'm planning on making a theme-store, we'll put your theme on there.
Would you like me to handle this for you? I've already cloned the theme into a repo, but if you'd like to publish it under your name we can do that too!