refactor(drivers): organize backup modules into drivers subfolder

- Move all backup_*.py files to libtisbackup/drivers/ subdirectory
- Move XenAPI.py and copy_vm_xcp.py to drivers/ (driver-specific)
- Create drivers/__init__.py with automatic driver imports
- Update tisbackup.py imports to use new structure
- Add pyvmomi>=8.0.0 as mandatory dependency
- Sync requirements.txt with pyproject.toml dependencies
- Add pylint>=3.0.0 and pytest-cov>=6.0.0 to dev dependencies
- Configure pylint and coverage tools in pyproject.toml
- Add conventional commits guidelines to CLAUDE.md
- Enhance .gitignore with comprehensive patterns for Python, IDEs, testing, and secrets
- Update CLAUDE.md documentation with new structure and tooling

Breaking Changes:
- Drivers must now be imported from libtisbackup.drivers instead of libtisbackup
- All backup driver files relocated to drivers/ subdirectory

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/README.md

@@ -0,0 +1,145 @@
+# TISBackup Test Suite
+
+This directory contains the test suite for TISBackup using pytest.
+
+## Running Tests
+
+### Run all tests
+```bash
+uv run pytest
+```
+
+### Run tests for a specific module
+```bash
+uv run pytest tests/test_ssh.py
+```
+
+### Run with verbose output
+```bash
+uv run pytest -v
+```
+
+### Run tests matching a pattern
+```bash
+uv run pytest -k "ssh" -v
+```
+
+### Run with coverage (requires pytest-cov)
+```bash
+uv run pytest --cov=libtisbackup --cov-report=html
+```
+
+## Test Structure
+
+### Current Test Modules
+
+- **[test_ssh.py](test_ssh.py)** - Tests for SSH operations module
+  - `TestLoadSSHPrivateKey` - Tests for key loading with Ed25519, ECDSA, and RSA support
+  - `TestSSHExec` - Tests for remote command execution via SSH
+  - `TestSSHModuleIntegration` - Integration tests for SSH functionality
+
+## Test Categories
+
+Tests are organized using pytest markers:
+
+- `@pytest.mark.unit` - Unit tests for individual functions
+- `@pytest.mark.integration` - Integration tests for multiple components
+- `@pytest.mark.ssh` - SSH-related tests
+- `@pytest.mark.slow` - Long-running tests
+
+### Run only unit tests
+```bash
+uv run pytest -m unit
+```
+
+### Run only SSH tests
+```bash
+uv run pytest -m ssh
+```
+
+## Writing New Tests
+
+### Test File Naming
+- Test files should be named `test_*.py`
+- Place them in the `tests/` directory
+
+### Test Class Naming
+- Test classes should start with `Test`
+- Example: `TestMyModule`
+
+### Test Function Naming
+- Test functions should start with `test_`
+- Use descriptive names: `test_load_ed25519_key_success`
+
+### Example Test Structure
+```python
+import pytest
+from libtisbackup.mymodule import my_function
+
+class TestMyFunction:
+    """Test cases for my_function."""
+
+    def test_basic_functionality(self):
+        """Test basic use case."""
+        result = my_function("input")
+        assert result == "expected_output"
+
+    def test_error_handling(self):
+        """Test error handling."""
+        with pytest.raises(ValueError):
+            my_function(None)
+```
+
+## Mocking
+
+The test suite uses `pytest-mock` for mocking dependencies. Common patterns:
+
+### Mocking with patch
+```python
+from unittest.mock import patch, Mock
+
+def test_with_mock():
+    with patch('module.function') as mock_func:
+        mock_func.return_value = "mocked"
+        result = my_code()
+        assert result == "mocked"
+```
+
+### Using pytest fixtures
+```python
+@pytest.fixture
+def mock_ssh_client():
+    return Mock(spec=paramiko.SSHClient)
+
+def test_with_fixture(mock_ssh_client):
+    # Use the fixture
+    pass
+```
+
+## Coverage Goals
+
+Aim for:
+- **80%+** overall code coverage
+- **90%+** for critical modules (ssh, database, base_driver)
+- **100%** for utility functions
+
+## Test Configuration
+
+Test configuration is in the `[tool.pytest.ini_options]` section of [pyproject.toml](../pyproject.toml):
+- Test discovery patterns
+- Output formatting
+- Markers definition
+- Minimum Python version
+
+## Continuous Integration
+
+Tests should pass before merging:
+```bash
+# Run linting
+uv run ruff check .
+
+# Run tests
+uv run pytest -v
+
+# Both must pass
+```