feat: add AlternateAppIconSettings for low-profile home icons

Persist the chosen catalog icon and apply it via setAlternateIconName,
with a panic-wipe reset path that restores the primary glyph.

bitchat/Services/AlternateAppIconSettings.swift

@@ -0,0 +1,121 @@
+//
+// AlternateAppIconSettings.swift
+// bitchat
+//
+// This is free and unencumbered software released into the public domain.
+// For more information, see <https://unlicense.org>
+//
+
+import Foundation
+#if os(iOS)
+import UIKit
+#endif
+import BitLogger
+
+/// Low-profile alternate home-screen icons (#1447). Neutral / notes / quiet
+/// variants live as App Icon sets in the asset catalog and are enabled via
+/// `ASSETCATALOG_COMPILER_INCLUDE_ALL_APPICON_ASSETS`.
+enum AlternateAppIconSettings {
+    static let storageKey = "appearance.alternateAppIcon"
+
+    /// Catalog names. `nil` means the primary AppIcon.
+    enum Icon: String, CaseIterable, Identifiable {
+        case primary
+        case neutral = "AppIconNeutral"
+        case notes = "AppIconNotes"
+        case quiet = "AppIconQuiet"
+
+        var id: String { rawValue }
+
+        /// Name passed to `UIApplication.setAlternateIconName`. Primary is nil.
+        var systemName: String? {
+            switch self {
+            case .primary: return nil
+            case .neutral, .notes, .quiet: return rawValue
+            }
+        }
+
+        var title: String {
+            switch self {
+            case .primary:
+                return String(
+                    localized: "app_info.settings.icon.primary",
+                    defaultValue: "bitchat",
+                    comment: "Label for the default bitchat home-screen icon"
+                )
+            case .neutral:
+                return String(
+                    localized: "app_info.settings.icon.neutral",
+                    defaultValue: "neutral",
+                    comment: "Label for the grayscale low-profile alternate app icon"
+                )
+            case .notes:
+                return String(
+                    localized: "app_info.settings.icon.notes",
+                    defaultValue: "notes",
+                    comment: "Label for the blue-gray notes-like alternate app icon"
+                )
+            case .quiet:
+                return String(
+                    localized: "app_info.settings.icon.quiet",
+                    defaultValue: "quiet",
+                    comment: "Label for the dark monochrome alternate app icon"
+                )
+            }
+        }
+    }
+
+    static var selected: Icon {
+        get { selected(in: .standard) }
+        set { setSelected(newValue, in: .standard, applySystem: true) }
+    }
+
+    static func selected(in defaults: UserDefaults) -> Icon {
+        let raw = defaults.string(forKey: storageKey) ?? Icon.primary.rawValue
+        return Icon(rawValue: raw) ?? .primary
+    }
+
+    static func setSelected(_ icon: Icon, in defaults: UserDefaults, applySystem: Bool = true) {
+        if icon == .primary {
+            defaults.removeObject(forKey: storageKey)
+        } else {
+            defaults.set(icon.rawValue, forKey: storageKey)
+        }
+        if applySystem {
+            apply(icon)
+        }
+    }
+
+    /// Apply the stored preference to the system (iOS only). Safe no-op elsewhere.
+    static func applyStoredPreference() {
+        apply(selected(in: .standard))
+    }
+
+    static func reset(in defaults: UserDefaults = .standard) {
+        defaults.removeObject(forKey: storageKey)
+        apply(.primary)
+    }
+
+    private static func apply(_ icon: Icon) {
+        #if os(iOS)
+        // Unit tests and early launch may not have a ready UIApplication.
+        guard Thread.isMainThread else {
+            DispatchQueue.main.async { apply(icon) }
+            return
+        }
+        guard UIApplication.shared.supportsAlternateIcons else { return }
+        let target = icon.systemName
+        // Avoid a no-op system prompt when already on the desired icon.
+        let current = UIApplication.shared.alternateIconName
+        guard current != target else { return }
+        UIApplication.shared.setAlternateIconName(target) { error in
+            if let error {
+                SecureLogger.warning(
+                    "alternate icon change failed: \(error.localizedDescription)",
+                    category: .session
+                )
+            }
+        }
+        #endif
+    }
+}