[Feature] Test environment login bypass for automation

[crazygo]

Description

The project currently uses GitHub OAuth for authentication. However, this login method is inconvenient for automated testing because:

1. In virtual/test environments, GitHub is not logged in
2. Cannot automatically bypass OAuth authorization flow
3. Test accounts need a way to access the main application without manual OAuth

We need a solution to allow test accounts to log in through an alternative mechanism in test environments.

Technical Approach

Environment Variable + Test Token Injection

Core idea: Inject a test JWT token via environment variable, bypassing OAuth in test environments.

1. Extend AuthService: Read token from environment variable BRICKS_TEST_TOKEN first
2. Add isTestMode(): Detect if running in test environment
3. Adapt LoginScreen: Show quick login entry in test mode
4. Run command: flutter test --dart-define=BRICKS_TEST_TOKEN=xxx

Security Considerations

• Test tokens should have limited permissions/validity
• isTestMode() check ensures test logic won't trigger in production
• Test tokens should be rotated regularly, not hardcoded

Acceptance Criteria

• AuthService supports reading test token from environment variable
• isTestMode() method correctly detects test environment
• LoginScreen can skip OAuth in test mode
• Test token can be injected via --dart-define
• Production environment is not affected (test logic disabled)
• Integration tests verify the complete flow

Related

• Thread: 1488041850974765056