Refresh the shared snapshot in the background so widgets stop going stale

publishWidgetSnapshot() only ever ran from a user action, so an event created
on the web or on Android did not reach the widgets until the app was opened
again. A BGAppRefreshTask now republishes without the foreground.

The two keys this needs are arrays, which Xcode does not expose as
INFOPLIST_KEY_ build settings — verified by building and inspecting the
result. Hence a partial Calendarr-Info.plist that generation merges into. It
sits at the project root rather than inside the target folder: that folder is
a synchronized group, which would also copy the file as a resource and collide
with the processed one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Calendarr iOS/CalendarrApp.swift

@@ -4,10 +4,17 @@ import SwiftUI
 struct CalendarrApp: App {
     @State private var appState = AppState()
 
+    init() {
+        // Registration has to happen before the app finishes launching, which
+        // is why it is here and not in a .task modifier.
+        BackgroundRefresh.register()
+    }
+
     var body: some Scene {
         WindowGroup {
             RootView()
                 .environment(appState)
+                .task { BackgroundRefresh.schedule() }
         }
     }
 }