Fix Facebook connection pending infinitely - implement OAuth support and improved timeouts

[Copilot]

The Facebook connection was getting stuck in a "pending" state indefinitely due to insufficient timeout handling and lack of proper OAuth authentication support. This PR addresses the root causes and provides a comprehensive solution.

🐛 Problem

Users experienced infinite pending states when attempting Facebook authentication, with no clear error messages or progress indication. The issue stemmed from:

• Short connection timeout (7 seconds) insufficient for OAuth flows
• Missing OAuth endpoints for social authentication
• Poor error handling with generic messages
• No progress indication during authentication flows

🔧 Solution

1. Extended Connection Timeouts

// Before: 7 seconds (too short for OAuth)
export const CONNECTION_TIMEOUT_MS = 7 * 1000;

// After: 30 seconds for standard connections, 60 seconds for OAuth
export const CONNECTION_TIMEOUT_MS = 30 * 1000;
export const OAUTH_TIMEOUT_MS = 60 * 1000;

2. OAuth Authentication Support

Added dedicated endpoints for social authentication:

// GET /auth/:provider - Initiate OAuth flow
// POST /auth/:provider/callback - Handle OAuth callback
// Supports Facebook and Google with proper state management

3. Enhanced Error Handling

// Before: Generic timeout error
reject(new Error(`Timeout while connecting to ${remoteServerUrl}`));

// After: Contextual error with guidance
reject(new Error(
  `Connection timeout after ${CONNECTION_TIMEOUT_MS / 1000} seconds. ` +
  `This may happen during social authentication flows like Facebook login. ` +
  `Please ensure stable network connection and complete authentication promptly.`
));

4. Connection Progress Utilities

Added comprehensive progress reporting system for frontend integration:

export function createConnectionProgressReporter(
  callback?: ConnectionProgressCallback
): ConnectionProgressCallback {
  // Provides real-time connection status updates
}

🧪 Testing

• ✅ Unit tests verify timeout configurations
• ✅ OAuth endpoints tested with mock authentication
• ✅ Error handling validated with various failure scenarios
• ✅ Progress reporting system tested
• ✅ All existing tests continue to pass

📊 Impact

• Resolves infinite pending state during Facebook OAuth flows
• Better user experience with clear progress indication and error messages
• Backward compatible - no breaking changes to existing API
• Configurable timeouts for different connection types
• Foundation for social authentication in Promptbook Studio

📝 Documentation

Added comprehensive documentation in FACEBOOK_CONNECTION_FIX.md including:

• Root cause analysis
• Implementation details
• Usage examples
• Troubleshooting guide
• Migration notes

Fixes #275.

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