# No external dependencies required - using only Python standard library
# All functionality is implemented using built-in modules:
# - sqlite3 for database operations
# - hashlib for password hashing
# - uuid for session/token generation  
# - datetime for timestamps
# - json for data serialization
# - re for regular expressions
# - os for file operations
# - tempfile for temporary files
# - base64 for encoding
# - unittest for testing