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/Settings/SettingsKey.swift

@@ -64,6 +64,7 @@ enum SettingsKey: String, CaseIterable {
     case homeShortcutOrder
     case homeShortcutVisibility
     case homeShortcutLayout
+    case homeShortcutCardStyle
     case homeSectionOrder
     case homeSectionVisibility
     case homeSectionItemsLimit
@@ -135,7 +136,7 @@ enum SettingsKey: String, CaseIterable {
         switch self {
         case .preferredQuality, .cellularQuality, .allowSoftwareDecodedFormats, .macPlayerMode, .listStyle,
              // Home layout — different UI paradigms per platform
-             .homeShortcutOrder, .homeShortcutVisibility, .homeShortcutLayout,
+             .homeShortcutOrder, .homeShortcutVisibility, .homeShortcutLayout, .homeShortcutCardStyle,
              .homeSectionOrder, .homeSectionVisibility, .homeSectionItemsLimit, .homeSectionLayout,
              // Top Shelf — tvOS only
              .topShelfSections,