Add retry exhaustion callback to RecommendationService

Summary

Add user-facing callback when WebSocket reconnection attempts are exhausted

Background

During code review of !7 (merged), jean_gabriel suggested adding a user notification when max retry attempts are exhausted. Currently the service silently stops retrying after 5 attempts.

Requirements

• Add callback interface for retry exhaustion
• Allow UI components to register listeners
• Include retry count and last error in callback
• Provide user-friendly error message suggestions

Proposed API

recommendationService.onRetryExhausted((error, attemptCount) => {
  // Show user notification
  showToast('Unable to connect to recommendation service. Please check your connection.');
});

Acceptance Criteria

• Callback interface defined
• UI hook implemented
• User notification shown
• Unit tests for callback behavior

Related Work

• Implemented in !7 (merged)
• Follow-up from code review discussion

Epic Context

mobile-section