Implement user activity logging for all user interactions

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This PR implements comprehensive user activity logging to satisfy the business requirement: "User activity shall be logged." The solution captures all user interactions and saves them to structured log files for analysis by log management systems.

Changes Made

New Logging System

• user_activity_logger.py: Complete logging utility with JSON-structured output, Flask integration for IP/User-Agent capture, and configurable log files
• tests/test_user_activity_logger.py: Comprehensive unit tests covering all logging scenarios
• LOGGING_README.md: Documentation for setup, configuration, and log management system integration

Updated Application

Modified wine.py to integrate logging at all user interaction points:

• Login attempts (successful and failed with failure reasons)
• User logout events
• Registration attempts with validation failure details
• Wine classification requests with complete input data and predictions
• Profile page access events
• Password change attempts with success/failure tracking
• Contact form submissions

Sample Log Output

{"timestamp": "2024-01-15T10:30:45.123456", "action": "login_attempt", "user_id": 123, "username": "johndoe", "ip_address": "192.168.1.100", "user_agent": "Mozilla/5.0...", "details": {"success": true, "attempted_username": "johndoe"}}

{"timestamp": "2024-01-15T10:35:12.789012", "action": "wine_classification", "user_id": 123, "username": "johndoe", "ip_address": "192.168.1.100", "user_agent": "Mozilla/5.0...", "details": {"wine_characteristics": {"alcohol": 12.5, "malic_acid": 2.3, ...}, "prediction": 1}}

Key Features

• Structured JSON format for easy parsing by log management systems (ELK Stack, Splunk, etc.)
• Comprehensive coverage of all user interactions as required
• Security-conscious design that avoids logging sensitive data like passwords
• Minimal code changes with surgical integration into existing application
• Analysis-ready logs with timestamps, user identification, IP addresses, and contextual details

The implementation ensures user actions are properly logged for audit trails and analysis while maintaining security best practices.

Fixes #1.

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