FretBoard: Chords & Scales

Changes: - Added tap-to-toggle notes: tap directly on the fretboard or on the dot area in the MagicNoteBar to customize scales and chords - Tap a scale note to mute it (appears translucent) - Tap an empty position to add a custom note (appears in purple) - Custom modifications affect both the visual display and audio playback - Reintroduced note shape customization from Classic FretBoard: long-press any note dot to change its shape - Choose from circle, square, diamond, cross (X), or triangle (up/down) shapes - Shapes are tied to scale degrees - when you change the root note, shapes follow their intervals - Shapes reset when selecting a different scale or chord - New "Shape of Root Note" setting in Appearance to set a default shape for all root notes - Redesigned settings and selection screens with new "Studio Glass" design system for improved usability and readability - Added tempo selection dialog with slider, tap tempo, and musical presets (Largo, Adagio, etc.) - BPM button now displays current tempo value - Reintroduced tap-to-hide HUD: tap anywhere on the fretboard to hide the bottom controls for an unobstructed view (a classic feature from the pre-Fretboard Evolution era) - Added User Guide in Settings explaining key features, note colors, playback controls, and gestures - Minimum iOS version changed from iOS 12 to iOS 16 Notes: This version is a native SwiftUI port of the original Flutter application. The iOS 16 requirement enables the use of modern SwiftUI features including Canvas-based rendering for improved fretboard visualization.