Add Integration Tests for User Flows

As we transition from prototype phase to production, we need to establish comprehensive integration tests to validate critical user flows. This will ensure that new developments do not introduce bugs or break existing features in OpenEO Studio.

Currently, the project relies primarily on manual QA. Without integration tests covering end-to-end user workflows, we risk:

- Undetected regressions when features interact with each other
- Difficulty identifying the root cause of issues spanning multiple components
- Reduced confidence in deployments and feature releases
- Poor test coverage for UI component interactions and data flow

## Goals

- Establish integration test coverage for critical user flows in the prototype phase
- Create a foundation for continuous testing of new features
- Document expected user behavior through test scenarios
- Enable safe refactoring and optimization of existing code
- Build confidence in the stability of core functionality

## Core User Flows to Test

### 1. **Data Loading & Scene Selection**

- User can load and view different satellite scenes
- Scene metadata is properly displayed
- Band information is correctly parsed and available

### 2. **Code Editor Workflow**

- User can write and edit code in the editor
- Code syntax validation works correctly
- Variables are available and can be selected via available variables panel
- Band array builder correctly constructs band selections

### 3. **Code Execution & Output**

- User can execute code against live data
- Output panel displays results correctly
- Errors are properly caught and displayed to the user
- Processing state is communicated to the user (loading, complete, error)

### 4. **Visualization**

- User can visualize processed output on the map
- Layer controls function properly
- Map interactions don't interfere with code editor

### 5. **Authentication & Session**

- User can authenticate successfully
- User info is displayed correctly
- Session state persists appropriately
- Logout functionality clears session state

## Tools & Framework

- **Test Framework**: Jest (already configured)
- **E2E Testing**: Consider Playwright for browser automation
- **API Mocking**: Mock STAC API responses and processing backends
- **Component Testing**: Test component integration with React Testing Library

## Acceptance Criteria

- [x] Integration test suite is set up and documented
- [ ] The critical user flow tests are implemented and passing
- [ ] Tests cover both happy path and error scenarios
- [x] Tests run in CI/CD pipeline on push
- [ ] Coverage targets are defined (minimum 70% for critical paths)

## Implementation Approach

1. **Setup Test Infrastructure**
- Configure E2E testing framework
- Set up test utilities and helpers
- Mock external API dependencies

2. **Implement Test Scenarios**
- Start with core user flows listed above
- Include both success and failure cases
- Test data validation and error handling

3. **CI/CD Integration**
- Add test execution to pipeline
- Configure test reports and coverage tracking
- Set up notifications for test failures

4. **Documentation**
- Document how to run tests locally
- Provide guidelines for writing new tests
- Document test data and fixtures

## Additional Considerations

- **Performance**: Ensure integration tests don't significantly slow down development workflow
- **Maintenance**: Tests should be easy to update as features evolve
- **Isolation**: Tests should be independent and not affect each other
- **Flakiness**: Implement retry logic and proper wait strategies to reduce flaky tests
- **Parallel Execution**: Tests should be able to run in parallel when possible