Add comprehensive testing infrastructure with Jest and React Testing Library

[Copilot]

This PR implements a complete testing setup for the event ticketing application to address the testing requirements outlined in the issue.

What's Added

Testing Infrastructure:

• Jest configuration with Next.js support and custom test environment
• React Testing Library for component testing with accessibility-first approach
• Comprehensive mocking setup for Convex backend, Next.js router, and toast notifications
• Custom jest.setup.js with global test configuration and mock implementations

Test Coverage:
The PR includes 25 tests across 4 test suites covering the core application functionality:

• JoinQueue Component (8 tests): User authentication flows, event ownership checks, sold-out scenarios, expired offers, and ticket purchase interactions
• EventCard Component (9 tests): Event display logic, user permissions, ticket status rendering, past/future event handling, and navigation
• PurchaseTicket Component (4 tests): Conditional rendering based on authentication and queue status
• Utility Functions (4 tests): Class name merging utility with edge cases

Key Features Tested

The test suite validates critical user flows including:

• User authentication and authorization
• Event ownership permissions and restrictions
• Ticket availability and waiting list management
• Queue position tracking and offer expiration
• Sold-out event handling
• Component conditional rendering based on user state
• Navigation and user interactions

Technical Implementation

// Example test structure
describe('JoinQueue Component', () => {
  it('shows "cannot buy ticket for own event" for event owner', () => {
    // Mock event owner scenario
    mockUseQuery
      .mockReturnValueOnce(mockUser)
      .mockReturnValueOnce(mockEvent) // user is owner

    render(<JoinQueue eventId={mockEventId} userId={mockUserId} />)
    
    expect(screen.getByText('You cannot buy a ticket for your own event')).toBeInTheDocument()
  })
})

All tests pass successfully, and the project continues to build and lint without issues. The testing infrastructure is now ready for future development and provides confidence in the application's core functionality.

Fixes #3.

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