Fix hardcoded paths in ledger configuration

[scottbrown]

Problem

The ledger configuration contains hardcoded absolute paths that make it non-portable across different systems and users.

Current Issues

• Hardcoded absolute path to ledger files
• Year-specific file references that require manual updates

Solution

• Use relative paths or environment variables for ledger file locations
• Create flexible configuration that supports multiple ledger files
• Add year-agnostic configuration options

Benefits

• Portable configuration across different systems
• Flexible ledger file organization
• Reduced manual maintenance
• Better user experience for new installations

Implementation Notes

• Use LEDGER_FILE environment variable for primary ledger file
• Support multiple ledger file configurations
• Consider using XDG Base Directory specification for file locations
• Add documentation for ledger file organization