[Frontend]: Add automated tests for chat user journey

[Hanseooo]

Problem

The chat flow will become multi-step and stateful; without tests, regressions are likely when backend contracts evolve.

Scope

• Add frontend tests (component/integration) for:
  • Initial send -> clarification response
  • Clarification submit -> itinerary response
  • Error handling and retry behavior
  • Session recovery / reset behavior
• Mock API responses with current backend contracts.

Acceptance Criteria

• Core chat journey is covered by stable tests.
• Tests fail when response contract handling breaks.

Priority

Quality

Dependencies

• Depends on: [Frontend]: Implement chat API client and React Query hooks #25, [Frontend]: Build clarification question flow in ChatPage #26, [Frontend]: Render itinerary results from AI response #27, [Frontend]: Add chat session lifecycle and recovery UX #28
• Blocking: blocks confident iteration/release of chat UX