- Fix error string capitalization to follow Go guidelines (ST1005)
- Fix unchecked error returns in test files (errcheck)
- Replace nil-nil return with proper error for non-TuneIn URLs (nilnil)
- Add missing comments for exported service type constants (revive)
- Rename unused parameters to underscore in test handlers (revive)
- Add t.Helper() calls to test helper functions (thelper)
- Update test expectations to match lowercase error messages
This addresses all critical linting issues while maintaining functionality.