dark mode and theme consistency fix

[Birdmannn]

Account Type Theme Alignment

Summary

Updated the account-type onboarding screen to match the creator dashboard's dark product UI and remove the visual jump between onboarding and the app.

What Changed

• Switched the page background to the dashboard-style dark base (#0b0a11)
• Reworked the main container into a dark bordered panel with subtle depth
• Converted role cards from light surfaces to dark dashboard-style cards
• Applied purple accent states for selection, hover, and CTA styling
• Updated the benefits section to use a darker inset surface
• Improved text contrast for headings, descriptions, and list items

File Updated

• frontend/src/features/onboarding/role-selection.tsx

Outcome

The onboarding flow now feels visually consistent with the creator/hunter dashboards, with readable text and no jarring theme shift after role selection.

Closes #246