UOW-013: Add Comprehensive Tests for XDG Package (0% Coverage)

[andhijeannot]

Overview

Phase: 5 - Testing
Priority: Medium
Estimated Effort: 4-6 hours

Problem Description

The XDG package currently has 0% test coverage, which is problematic for cross-platform compatibility and directory management functions.

Acceptance Criteria

• Achieve >95% test coverage for XDG package
• Test all XDG Base Directory Specification functions
• Cross-platform compatibility tests (Windows, macOS, Linux)
• Edge case testing (permissions, missing directories, invalid paths)
• Environment variable override testing

Files to Modify

• internal/xdg/xdg_test.go (new file)
• internal/xdg/testdata/ (new test fixtures)

See roadmap/phase5-testing/UOW-013-xdg-testing.md for detailed implementation plan.