Yattee v2 rewrite

Yattee/Views/Components/ListBackgroundStyle.swift

@@ -0,0 +1,58 @@
+//
+//  ListBackgroundStyle.swift
+//  Yattee
+//
+//  Platform-specific background colors for list containers.
+//
+
+import SwiftUI
+
+/// Background style variants for list containers.
+///
+/// Provides consistent platform-specific colors for grouped lists,
+/// plain lists, and card backgrounds across iOS, macOS, and tvOS.
+enum ListBackgroundStyle {
+    /// Grouped background (systemGroupedBackground on iOS).
+    /// Used as outer background for inset list style.
+    case grouped
+
+    /// Plain background (systemBackground on iOS).
+    /// Used as outer background for plain list style.
+    case plain
+
+    /// Card/row background (secondarySystemGroupedBackground on iOS).
+    /// Used for the card container in inset list style.
+    case card
+
+    /// Returns the platform-appropriate color for this background style.
+    var color: Color {
+        switch self {
+        case .grouped:
+            #if os(iOS)
+            Color(uiColor: .systemGroupedBackground)
+            #elseif os(macOS)
+            Color(nsColor: .windowBackgroundColor)
+            #else
+            Color.black.opacity(0.9)
+            #endif
+
+        case .plain:
+            #if os(iOS)
+            Color(uiColor: .systemBackground)
+            #elseif os(macOS)
+            Color(nsColor: .windowBackgroundColor)
+            #else
+            Color.clear
+            #endif
+
+        case .card:
+            #if os(iOS)
+            Color(uiColor: .secondarySystemGroupedBackground)
+            #elseif os(macOS)
+            Color(nsColor: .controlBackgroundColor)
+            #else
+            Color.gray.opacity(0.2)
+            #endif
+        }
+    }
+}