Fix map rendering and add error handling

[kdsmith10000]

Summary

• Fix Zoom_start to zoom_start - This case-sensitive typo was causing the map to render blank
• Add comprehensive error handling - The app now gracefully handles invalid phone numbers, failed geocoding, and missing results instead of crashing silently
• Improve phone number parsing - Auto-adds + prefix for numbers starting with a digit, and uses US as a fallback region
• Fix open_map() function - Uses absolute file path so the HTML file opens correctly regardless of working directory
• Add API key documentation - Added comment clarifying the API key must be kept in quotes

Changes

• Fixed folium Map parameter from Zoom_start=9 to zoom_start=9
• Added try/except blocks with user-friendly error messages
• Added input validation and sanitization
• Improved the open_map() function to check if file exists before opening

Test plan

• Enter a valid phone number with country code (e.g., +14155551234)
• Enter a phone number without + prefix (e.g., 14155551234)
• Enter an invalid phone number to verify error handling
• Click "Location" button to verify map opens correctly
• Verify map is no longer blank