feat(apple/M1+M3+M4): widgets, Live Activity, and Siri/Shortcuts intents

The extension-side + App Intents surface for design/apple-live-activities-and-
widgets.md. The iOS-framework code (WidgetKit/ActivityKit/AppIntents) can't be
compiled by the macOS `swift build` CI target and needs the Xcode widget-
extension target that only exists once created in the GUI — see the checklist in
the memory note. What macOS DID verify: HostEntity (AppIntents is available on
macOS), the shared attribute/notification plumbing, and that nothing regressed
(142 tests green).

Shared (PunktfunkShared):
- PunktfunkSessionAttributes (ActivityAttributes) — the one type app + extension
  share; gated os(iOS) (ActivityKit imports on macOS but its types are
  unavailable, so canImport would wrongly admit it).
- EndStreamIntent (LiveActivityIntent) — posts .punktfunkEndActiveSession.
- HostEntity + HostEntityQuery (AppEntity over the shared store) — the intent /
  widget-config parameter type; canImport(AppIntents), so macOS type-checks it.
- New notifications: end-active-session, open-deep-link.

M1 widget extension sources (Sources/PunktfunkWidgets/, NOT a SwiftPM target —
`swift build` ignores the dir):
- PunktfunkWidgetBundle (@main): HostsWidget + PunktfunkSessionLiveActivity.
- HostsWidget (kind "PunktfunkHosts"): reads the shared-suite store, sorts by
  recency, deep-links each host; small/medium/accessory families; empty state.
- SessionLiveActivity: Lock-Screen banner + Dynamic Island (elapsed timer,
  mode line, background countdown, End button).

M3 controller (app, iOS): SessionActivityController owns the Activity lifecycle
(request/update/end + launch orphan-sweep + staleDate); ContentView drives it
from the model's phase/isBackgrounded/backgroundDeadline (which SessionModel now
publishes), keeping ActivityKit out of the cross-platform model.

M4 (app, iOS): ConnectToHost/WakeHost intents + AppShortcutsProvider; Connect
routes via .punktfunkOpenDeepLink into the same onOpenURL router (one set of
guards); Wake reuses the WoL path; End surfaced to Shortcuts too.

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

clients/apple/Sources/PunktfunkClient/Session/SessionModel.swift

@@ -152,6 +152,9 @@ final class SessionModel: ObservableObject {
     /// (audio plays, video dropped, timeout armed). Drives the Live Activity's stage/countdown (M3)
     /// and is cleared on foreground or teardown. iOS/iPadOS only in practice.
     @Published private(set) var isBackgrounded = false
+    /// When the backgrounded keep-alive will auto-disconnect (nil unless backgrounded) — drives the
+    /// Live Activity countdown. Set alongside `backgroundTimer`.
+    @Published private(set) var backgroundDeadline: Date?
     /// Bounded auto-disconnect for a backgrounded keep-alive session. Fires on `.main`.
     private var backgroundTimer: DispatchSourceTimer?
 
@@ -353,6 +356,7 @@ final class SessionModel: ObservableObject {
         // Non-deliberate on fire (keep the host linger) so a user who returns late reconnects fast,
         // exactly like today's network-drop path. min 1 minute guards a nonsense setting.
         let minutes = max(1, timeoutMinutes)
+        backgroundDeadline = Date().addingTimeInterval(TimeInterval(minutes * 60))
         let timer = DispatchSource.makeTimerSource(queue: .main)
         timer.schedule(deadline: .now() + .seconds(minutes * 60))
         timer.setEventHandler { [weak self] in
@@ -370,6 +374,7 @@ final class SessionModel: ObservableObject {
     func exitBackground() {
         guard isBackgrounded else { return }
         isBackgrounded = false
+        backgroundDeadline = nil
         backgroundTimer?.cancel()
         backgroundTimer = nil
         audio?.setMicMuted(false)
@@ -400,6 +405,7 @@ final class SessionModel: ObservableObject {
         backgroundTimer?.cancel()
         backgroundTimer = nil
         isBackgrounded = false
+        backgroundDeadline = nil
         let audio = self.audio
         self.audio = nil
         // Gamepad capture is main-actor (releases held buttons on the wire while the