Use design tokens for notification badge colors

[vku2018]

Summary

• replace the notification badge's hardcoded inline hex/fallback colors with variant-specific design tokens
• add landing-page danger/on-danger tokens alongside the existing landing token set
• make the dashboard notification badge use the existing --dash-danger and --dash-on-danger token pair

This finishes the token-system acceptance item for the notification bell implementation currently on main.

Closes #58.

Validation

• git diff --check passes
• apps/frontend/node_modules/.bin/tsc.CMD --noEmit runs, but the repo currently fails on pre-existing unrelated errors:
  • app/dashboard/creator/campaigns/[id]/page.tsx: missing @/components/dashboard/creator/dashboard-header
  • app/dashboard/creator/campaigns/page.tsx: CampaignListRow receives unsupported onClick
• next lint is not available as a Next 16 subcommand in this repo; direct ESLint currently fails during config loading with an existing circular config serialization error before reaching changed files

[vercel]

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