Implement Farcaster authentication alongside Privy

[theref]

Overview

Add Farcaster authentication support without removing Privy, allowing both authentication methods to coexist for different environments.

Tasks

• Install additional dependencies (wagmi for wallet connections)
• Create Farcaster authentication service
• Implement "Sign in with Farcaster" flow
• Add Farcaster user data handling
• Create authentication method selector
• Update AuthContext to support dual authentication
• Add authentication state management for both methods

Implementation Details

interface AuthState {
  method: 'privy' | 'farcaster';
  user: FarcasterUser | PrivyUser | null;
  isAuthenticated: boolean;
}

interface FarcasterUser {
  fid: number;
  username: string;
  displayName: string;
  pfpUrl: string;
  bio: string;
}

Acceptance Criteria

• Farcaster authentication works in Mini App environment
• Privy authentication continues to work in regular browser
• AuthContext properly handles both authentication methods
• User data is consistent regardless of auth method
• Authentication state is properly managed
• No breaking changes to existing auth-dependent code

Priority

High - Core authentication functionality

Dependencies

• Issue Setup Farcaster Mini App environment detection #16 (Environment detection) must be completed first

Testing

• Test Farcaster auth in Mini App environment
• Test Privy auth in regular browser
• Test auth state persistence
• Test user data retrieval for both methods