Redesign Login/Signup Page (Modern UI with GitHub OAuth) #110

Context

Update the login page to a modern, centered modal design with a dotted background (inspired by modern dev tools). Since Codra only supports GitHub auth, adapt the reference design to show only the GitHub login option.

Reference Design

Task

1. Background: Full-screen dark theme with a subtle dotted grid pattern.
2. Modal: Centered card with rounded corners, subtle border, and shadow.
3. Content:
   • Circular logo at the top.
   • Title ("Sign in to Codra") and subtitle.
   • Primary Action: A single, full-width "Continue with GitHub" button.
   • Footer: Muted Terms of Service / Privacy Policy text at the bottom.
4. Omit: Do not include the email input, Google, or Apple buttons seen in the reference.
5. Responsiveness: Ensure proper padding and scaling on mobile devices.

Acceptance Criteria

• UI matches the aesthetic of the reference design.
• Displays only the GitHub OAuth button.
• Clicking the button correctly initiates the existing OAuth flow.
• Layout is fully responsive on mobile screens.

Relevant Files/Paths

• apps/dashboard/src/ (Login page route)