feat: enhance security with improved password hashing and logging

- Add Argon2PasswordHasher with high security settings as primary hasher
- Implement fallback to PBKDF2PasswordHasher for CentOS 7/Python 3.6 compatibility
- Add argon2-cffi dependency to requirements.txt
- Replace all print statements with proper logging calls across codebase
- Implement comprehensive logging configuration with multiple handlers:
  * ivatar.log - General application logs (INFO level)
  * ivatar_debug.log - Detailed debug logs (DEBUG level)
  * security.log - Security events (WARNING level)
- Add configurable LOGS_DIR setting with local config override support
- Create config_local.py.example with logging configuration examples
- Fix code quality issues (flake8, black formatting, import conflicts)
- Maintain backward compatibility with existing password hashes

Security improvements:
- New passwords use Argon2 (memory-hard, ASIC-resistant)
- Enhanced PBKDF2 iterations for fallback scenarios
- Structured logging for security monitoring and debugging
- Production-ready configuration with flexible log locations

Tests: 85/113 passing (failures due to external DNS/API dependencies)
Code quality: All pre-commit hooks passing

config_local.py.example

@@ -0,0 +1,41 @@
+# -*- coding: utf-8 -*-
+"""
+Example local configuration file for ivatar
+Copy this to config_local.py and customize for your environment
+"""
+
+import os
+
+# Override logs directory for production deployments
+# LOGS_DIR = "/var/log/ivatar"
+
+# Override logs directory for development with custom location
+# LOGS_DIR = os.path.join(os.path.expanduser("~"), "ivatar_logs")
+
+# Example production overrides:
+# DEBUG = False
+# SECRET_KEY = "your-production-secret-key-here"
+# ALLOWED_HOSTS = ["yourdomain.com", "www.yourdomain.com"]
+
+# Database configuration (if not using environment variables)
+# DATABASES = {
+#     'default': {
+#         'ENGINE': 'django.db.backends.postgresql',
+#         'NAME': 'ivatar_prod',
+#         'USER': 'ivatar_user',
+#         'PASSWORD': 'your-db-password',
+#         'HOST': 'localhost',
+#         'PORT': '5432',
+#     }
+# }
+
+# Email configuration
+# EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
+# EMAIL_HOST = 'smtp.yourdomain.com'
+# EMAIL_PORT = 587
+# EMAIL_USE_TLS = True
+# EMAIL_HOST_USER = 'noreply@yourdomain.com'
+# EMAIL_HOST_PASSWORD = 'your-email-password'
+
+# Example: Override logs directory for production
+# LOGS_DIR = "/var/log/ivatar"