Code hygiene: Tests and issues

[ghostleek]

Issues Identified:

1. Database Connection Management:
   - Repetitive connection/close patterns
   - No connection pooling
   - Mixed database logic in multiple files
2. Large Monolithic Functions:
   - process_pdf.py has very long methods
   - sidebar.py has complex nested logic
   - Mixed concerns (UI + business logic)
3. Error Handling:
   - Inconsistent error handling patterns
   - Limited logging strategy
   - No centralized exception handling
4. Configuration Management:
   - Hard-coded values scattered throughout
   - No centralized config management
5. Testing:
   - No existing unit tests
   - No integration tests
   - No test data management