Add card style option for Home shortcut cards

Adds a Style picker (Plain / Accent / Colorful) to the Customize Home
sheet, shown when the shortcuts layout is Cards. Defaults to Plain.

- Plain: current look (light accent tint + accent border)
- Accent: solid accent fill, white icon/text
- Colorful: solid fill with a fixed color per shortcut type

The filled styles use a Reminders-style layout (icon top-leading, count
top-trailing, title anchored to the bottom) with a subtle gradient sheen
over the fill color. Cards without a meaningful count (Open Link, Remote,
Subscriptions, instance content, media sources) hide the number; Remote
shows its status dot in the top-right slot instead.

Persisted via SettingsKey.homeShortcutCardStyle, mirroring the existing
homeShortcutLayout accessor.

Yattee/Core/SettingsManager.swift

@@ -108,6 +108,7 @@ final class SettingsManager {
     var _homeShortcutOrder: [HomeShortcutItem]?
     var _homeShortcutVisibility: [HomeShortcutItem: Bool]?
     var _homeShortcutLayout: HomeShortcutLayout?
+    var _homeShortcutCardStyle: HomeShortcutCardStyle?
     var _homeSectionOrder: [HomeSectionItem]?
     var _homeSectionVisibility: [HomeSectionItem: Bool]?
     var _homeSectionItemsLimit: Int?
@@ -463,6 +464,7 @@ final class SettingsManager {
         _homeShortcutOrder = nil
         _homeShortcutVisibility = nil
         _homeShortcutLayout = nil
+        _homeShortcutCardStyle = nil
         _homeSectionOrder = nil
         _homeSectionVisibility = nil
         _homeSectionItemsLimit = nil