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/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>