feat(security): add audit logging for shlex fallback parser

- Add debug logging when shlex fallback extraction is used, capturing
  both successful extractions and failures for security auditing
- Add test case for docker nested quotes that trigger fallback parser
- Remove redundant comment about re import (already at module level)

Follow-up improvements from PR #127 code review:
- Enables tracking of malformed command patterns in production logs
- Verifies fallback parser handles the exact docker exec case reported

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test_security.py

@@ -107,6 +107,8 @@ def test_extract_commands():
         ("/usr/bin/node script.js", ["node"]),
         ("VAR=value ls", ["ls"]),
         ("git status || git init", ["git", "git"]),
+        # Fallback parser test: complex nested quotes that break shlex
+        ('docker exec container php -r "echo \\"test\\";"', ["docker"]),
     ]
 
     for cmd, expected in test_cases: