feat: calorie ring widget — home screen + lock screen

Widget displays:
- systemSmall: calorie ring + "X left" text
- systemMedium: ring + "Calories" / "X of Y" / "X remaining"
- accessoryCircular: gauge ring for lock screen
- accessoryInline: "🔥 845 / 2000 cal" text for lock screen
- accessoryRectangular: linear gauge + calorie count

Data flow: main app writes totalCalories + calorieGoal to
UserDefaults on each loadTodayData(), then calls
WidgetCenter.shared.reloadAllTimelines(). Widget reads on
15-minute refresh cycle.

Note: currently uses standard UserDefaults (same app container).
For production, migrate to App Group UserDefaults so widget
process can read the data. Requires Xcode App Group setup.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ios/Platform/Platform/Features/Home/HomeViewModel.swift

@@ -1,5 +1,6 @@
 import SwiftUI
 import PhotosUI
+import WidgetKit
 
 @Observable
 final class HomeViewModel {
@@ -32,6 +33,11 @@ final class HomeViewModel {
         totalCalories = repo.entries.reduce(0) { $0 + $1.snapshotCalories }
         calorieGoal = repo.goal?.calories ?? 2000
         isLoading = false
+
+        // Write to UserDefaults for widget
+        UserDefaults.standard.set(totalCalories, forKey: "widget_totalCalories")
+        UserDefaults.standard.set(calorieGoal, forKey: "widget_calorieGoal")
+        WidgetCenter.shared.reloadAllTimelines()
     }
 
     // MARK: - Background Image