test: Enhanced integration testing

[db-tycoon-stephen]

Summary

Expand integration test coverage for CLI commands and SnowDDL workflows.

Motivation

From roadmap Priority 2 and Technical Debt:

• Current test coverage ~40%, target >80%
• Limited integration tests
• Missing end-to-end tests

Proposed Test Suites

tests/integration/
├── test_cli_snowddl_integration.py   # CLI <-> SnowDDL interaction
├── test_authentication_methods.py     # RSA keys, encrypted passwords
├── test_deployment_workflow.py        # Plan -> Apply flow
└── test_yaml_validation.py            # Config validation

Test Scenarios

1. CLI Integration

   • snowddl-plan produces expected output format
   • snowddl-apply with --dry-run mode
   • Error handling for missing configs

2. Authentication

   • RSA key generation and validation
   • Password encryption/decryption roundtrip
   • Fernet key handling

3. Workflow

   • Full plan -> review -> apply cycle (mocked)
   • Rollback scenarios
   • Concurrent modification handling

Acceptance Criteria

• Test coverage increased to >60%
• All new tests pass in CI
• Integration tests isolated (no real Snowflake calls)
• Tests documented in TESTING.md

[db-tycoon-stephen]

Completed in PR #26 (merged to v0.3)