Add igiRadio iOS/iPadOS app for DigiRadio control.

Introduces a new SwiftUI app with HTTP REST device control, mock mode for UI development, BLE-based discovery, and documented architecture aligned with the firmware API.

Co-authored-by: Cursor <cursoragent@cursor.com>

Software/APP/igiRadio/Documentation/UI_ARCHITECTURE.md

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+# UI_ARCHITECTURE — igiRadio
+
+## iPhone
+
+`TabView` con tab: Home, Radio, Presets, Audio, Settings.
+
+## iPad
+
+`NavigationSplitView`:
+- Sidebar: Home, FM, DAB, Presets, Bluetooth, Audio, Settings
+- Detail: contenuto selezionato
+
+## Schermate
+
+| Schermata | ViewModel |
+|-----------|-----------|
+| Connection | `ConnectionViewModel` |
+| Home | `HomeViewModel` |
+| FM | `FMViewModel` |
+| DAB | `DABViewModel` |
+| Presets | `PresetsViewModel` |
+| Audio | `AudioViewModel` |
+| Bluetooth | `BluetoothViewModel` |
+| Settings | `SettingsViewModel` |
+| Device Info | `DeviceViewModel` |
+| Diagnostics | `DiagnosticsViewModel` |
+| Firmware | `FirmwareViewModel` |
+
+## Design System
+
+`Components/DesignSystem/` — colori semantici, tipografia, card, slider, status dot.