Add Custom Tuning Creation

[pbalduino]

Description

Allow users to create and save custom tunings

Priority

🟢 Low

Category

Feature

Details

• Add 'Create Custom Tuning' option to tunings screen
• Allow users to set custom note names and frequencies
• Save custom tunings to local storage
• Provide validation for frequency ranges

Files Affected

• lib/screens/tunings_screen.dart
• lib/data/tunings.dart

Acceptance Criteria

• Users can create new custom tunings
• Custom tunings are saved and persist
• Tuning creation interface is intuitive
• Custom tunings appear in the tunings list

Task ID: FEATURE-001