Add position-based colorful Home shortcut palettes

Colorful shortcut cards now color by grid position instead of shortcut
identity, so colors stay in the same slot when shortcuts are reordered.

Adds a Palette option (Classic default, plus Sunset, Meadow, Berry,
Grape) and a Custom palette with a swatch-list editor (ColorPicker + hex
fields) and a switchable comma-separated text field. Color is resolved
per position and wraps by palette length, wired via a new
homeShortcutColorfulColor environment value and a Color(hex:) extension.

Yattee/Core/SettingsManager.swift

@@ -109,6 +109,8 @@ final class SettingsManager {
     var _homeShortcutVisibility: [HomeShortcutItem: Bool]?
     var _homeShortcutLayout: HomeShortcutLayout?
     var _homeShortcutCardStyle: HomeShortcutCardStyle?
+    var _homeShortcutColorfulPalette: HomeShortcutColorfulPalette?
+    var _homeShortcutCustomPaletteColors: [String]?
     var _homeSectionOrder: [HomeSectionItem]?
     var _homeSectionVisibility: [HomeSectionItem: Bool]?
     var _homeSectionItemsLimit: Int?
@@ -465,6 +467,8 @@ final class SettingsManager {
         _homeShortcutVisibility = nil
         _homeShortcutLayout = nil
         _homeShortcutCardStyle = nil
+        _homeShortcutColorfulPalette = nil
+        _homeShortcutCustomPaletteColors = nil
         _homeSectionOrder = nil
         _homeSectionVisibility = nil
         _homeSectionItemsLimit = nil