feat(frontend): add carrier certification upload and verification

[mijinummi]

🎯 Summary
Closes #881
Implements the carrier certification upload workflow within frontend/package/, enabling carriers to:

Upload certification documents
Track verification status
View uploaded certifications
Delete pending/rejected certifications
Re-upload corrected certifications

This closes a critical onboarding gap that previously prevented carriers from becoming verified.

Closes #882
Implements the Profile Settings page inside frontend/package/pages/settings/Profile/, allowing users to:

Update profile information
Upload and preview avatars
Receive email verification reminders
Save profile changes
Prevent accidental navigation with unsaved edits

All functionality remains strictly within frontend/package/ as required.

Closes #883
Implements a centralized WebSocket layer for the frontend package, providing:

Single shared Socket.io connection
JWT authentication from Zustand auth store
Subscription management API
Automatic listener cleanup
Exponential backoff reconnection
Connection status tracking
Shipment-specific convenience hook

This prevents duplicate socket connections across components and standardizes real-time communication throughout the application.

closes #884

Implements a production-ready Error Boundary system within frontend/package/ that:

Prevents entire page crashes from React render errors
Displays a friendly recovery interface
Supports custom fallback UIs
Logs errors in development
Provides a useErrorBoundary() hook for async/runtime errors
Includes demo usage wrapping three independent page sections

This improves resilience and user experience by allowing recovery from isolated UI failures without requiring a full page refresh.

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