page/login-page: build login screen with CTA

[Rend1027]

Create the login screen for LocalBeats Landing Page. This is the first screen users see when visiting the app.
(CTA-Call To Action)

• Display “Sign in with Spotify” button
• Connect button to OAuth redirect flow (can be stubbed if OAuth isn’t ready)
• Add short headline or pitch:
• “See what NYC is vibing to right now”
• Center content vertically (mobile-first design)
• Optional: add LocalBeats logo or color scheme for branding
• Add the background
• Fix the logo
• No nav bar, no login, no signup.