Added tool version information and last updated time display

Show version info in footer and sidebar for enhanced user experience

Created a beautiful changelog page

Optimized version info display style to be more prominent

🏠 Mortgage Calculator - Analyze mortgage rates, loan amounts, and loan terms to calculate monthly payments

💰 Loan Calculator - Personal loan calculation tool

🛒 Discount Calculator - Quick discount price calculation

💡 Electricity Cost Calculator - Calculate appliance power costs

📊 Unit Price Calculator - Product unit price comparison tool

🔄 Unit Converter - Energy and volume unit conversions

💵 Income Tax Calculator - After-tax income calculation

🌐 Bilingual support (English & Chinese)

📱 Responsive design with perfect mobile support