fix(apple/M3): import AppIntents for Button(intent:) + drop deprecated Text+

The Live Activity's End button uses Button(intent:), whose initializer lives in
_AppIntents_SwiftUI — reached via `import AppIntents` (was missing, so the
widget target failed to build). Also replaced the iOS-26-deprecated Text + Text
concatenation in the background countdown with an HStack.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/PunktfunkWidgets/SessionLiveActivity.swift

@@ -7,6 +7,7 @@
 // Text(timerInterval:) — no per-second push.
 
 import ActivityKit
+import AppIntents
 import SwiftUI
 import WidgetKit
 
@@ -104,10 +105,13 @@ private struct StageLine: View {
             EmptyView()
         case .background:
             if let deadline = state.backgroundDeadline {
-                Text("Keeps running for ")
+                HStack(spacing: 3) {
-                    .font(.caption2).foregroundStyle(.secondary)
+                    Text("Keeps running for")
-                    + Text(timerInterval: Date()...deadline, countsDown: true)
+                    Text(timerInterval: Date()...deadline, countsDown: true)
-                    .font(.caption2).monospacedDigit()
+                        .monospacedDigit()
+                }
+                .font(.caption2)
+                .foregroundStyle(.secondary)
             } else {
                 badge("Running in background", .orange)
             }

clients/apple/PunktfunkWidgetsExtension.entitlements

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict/>
+</plist>