feat(apple/M0): App Group + PunktfunkShared + punktfunk:// deep links

Foundation milestone for Live Activities & Widgets (design/apple-live-
activities-and-widgets.md). No user-visible change beyond the URL scheme.

- New dependency-free PunktfunkShared SwiftPM target (+ library product) so a
  future widget extension can link it WITHOUT PunktfunkKit (Rust staticlib +
  presentation layer). Moves StoredHost (model + JSON codec), DefaultsKeys, and
  punktfunkDefaultMgmtPort there; adds AppGroup.suiteName and the punktfunk://
  DeepLink builder/parser. PunktfunkKit @_exported-imports it (no call-site
  churn for consumers; intra-Kit files import it explicitly since imports are
  file-scoped).
- HostStore reads/writes the shared App-Group suite (group.io.unom.punktfunk)
  with a one-time migration from UserDefaults.standard (old value left in place
  for staged rollout); reloads the "PunktfunkHosts" widget timeline on change.
- App Group entitlement on iOS/tvOS + macOS.
- CFBundleURLTypes scheme `punktfunk`; ContentView.onOpenURL routes
  connect/<uuid>[?launch=<GameEntry.id>] into the existing connect() path
  (unknown host / already-streaming guards; never tears down a live session).
- Round-trip tests: StoredHost JSON codec (+ legacy missing-optional decode),
  DeepLink grammar. `swift build` + `swift test` green (142 tests, 0 failures).

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

clients/apple/Sources/PunktfunkKit/Gamepad/GamepadFeedback.swift

@@ -23,6 +23,7 @@ import Combine
 import CoreHaptics
 import Foundation
 import GameController
+import PunktfunkShared
 
 public final class GamepadFeedback {
     private let connection: PunktfunkConnection

clients/apple/Sources/PunktfunkKit/Gamepad/GamepadManager.swift

@@ -20,6 +20,7 @@
 import Combine
 import Foundation
 import GameController
+import PunktfunkShared
 
 @MainActor
 public final class GamepadManager: ObservableObject {

clients/apple/Sources/PunktfunkKit/Gamepad/GamepadUIEnvironment.swift

@@ -6,6 +6,7 @@
 // the two combine without adding a second ObservableObject or an environment key nobody else needs.
 
 import Foundation
+import PunktfunkShared
 
 public enum GamepadUIEnvironment {
     /// `enabledSetting` is the user's Settings toggle (`DefaultsKey.gamepadUIEnabled`);