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>

libtisbackup/ssh.py

@@ -0,0 +1,104 @@
+#!/usr/bin/python3
+# -*- coding: utf-8 -*-
+# -----------------------------------------------------------------------
+#    This file is part of TISBackup
+#
+#    TISBackup is free software: you can redistribute it and/or modify
+#    it under the terms of the GNU General Public License as published by
+#    the Free Software Foundation, either version 3 of the License, or
+#    (at your option) any later version.
+#
+#    TISBackup is distributed in the hope that it will be useful,
+#    but WITHOUT ANY WARRANTY; without even the implied warranty of
+#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#    GNU General Public License for more details.
+#
+#    You should have received a copy of the GNU General Public License
+#    along with TISBackup.  If not, see <http://www.gnu.org/licenses/>.
+#
+# -----------------------------------------------------------------------
+
+"""SSH operations and key management utilities."""
+
+import sys
+
+try:
+    sys.stderr = open("/dev/null")  # Silence silly warnings from paramiko
+    import paramiko
+except ImportError as e:
+    print(("Error : can not load paramiko library %s" % e))
+    raise
+
+sys.stderr = sys.__stderr__
+
+
+def load_ssh_private_key(private_key_path):
+    """Load SSH private key with modern algorithm support.
+
+    Tries to load the key in order of preference:
+    1. Ed25519 (most secure, modern)
+    2. ECDSA (secure, widely supported)
+    3. RSA (legacy, still secure with sufficient key size)
+
+    DSA is not supported as it's deprecated and insecure.
+
+    Args:
+        private_key_path: Path to the private key file
+
+    Returns:
+        paramiko key object
+
+    Raises:
+        paramiko.SSHException: If key cannot be loaded
+    """
+    key_types = [
+        ("Ed25519", paramiko.Ed25519Key),
+        ("ECDSA", paramiko.ECDSAKey),
+        ("RSA", paramiko.RSAKey),
+    ]
+
+    last_exception = None
+    for key_name, key_class in key_types:
+        try:
+            return key_class.from_private_key_file(private_key_path)
+        except paramiko.SSHException as e:
+            last_exception = e
+            continue
+
+    # If we get here, none of the key types worked
+    raise paramiko.SSHException(
+        f"Unable to load private key from {private_key_path}. "
+        f"Supported formats: Ed25519 (recommended), ECDSA, RSA. "
+        f"DSA keys are no longer supported. "
+        f"Last error: {last_exception}"
+    )
+
+
+def ssh_exec(command, ssh=None, server_name="", remote_user="", private_key="", ssh_port=22):
+    """execute command on server_name using the provided ssh connection
+    or creates a new connection if ssh is not provided.
+    returns (exit_code,output)
+
+    output is the concatenation of stdout and stderr
+    """
+    if not ssh:
+        assert server_name and remote_user and private_key
+        mykey = load_ssh_private_key(private_key)
+
+        ssh = paramiko.SSHClient()
+        ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
+        ssh.connect(server_name, username=remote_user, pkey=mykey, port=ssh_port)
+
+    tran = ssh.get_transport()
+    chan = tran.open_session()
+
+    # chan.set_combine_stderr(True)
+    chan.get_pty()
+    stdout = chan.makefile()
+
+    chan.exec_command(command)
+    stdout.flush()
+    output_base = stdout.read()
+    output = output_base.decode(errors="ignore").replace("'", "")
+    exit_code = chan.recv_exit_status()
+    return (exit_code, output)