Phase 4.A.1: Live Activity + Dynamic Island für laufende Gassi-Tour

Neues Widget-Extension-Target BanYaroGoWidgetExtension:
- Bundle-ID app.banyaro.ios.BanYaroGoWidget
- NSExtensionPointIdentifier = com.apple.widgetkit-extension
- Synced root group + explizite Info.plist + Embed-Phase in App-Target
- Cross-Membership der Shared/WalkActivityAttributes.swift in beiden Targets

Shared/WalkActivityAttributes.swift:
- ActivityAttributes mit startedAt (fix)
- ContentState mit distanceMeters, elapsedSeconds, pointCount, isPaused, isAutoPaused

BanYaroGoWidget/WalkLiveActivity.swift:
- Lock-Screen-View: Pfote-Icon + Status-Pille (Live/Pause/Auto-Pause) +
  Stats-Spalten (Distanz/Dauer/Punkte)
- Dynamic Island compact: Pfote leading, Distanz trailing
- Dynamic Island minimal: nur Pfote
- Dynamic Island expanded: Distanz/Dauer/Status mit Pfote zentriert

WalkActivityController:
- @MainActor Facade um ActivityKit
- start() prüft areActivitiesEnabled, killt orphaned current, request mit Initial-State
- update() async via Task
- end() mit dismissalPolicy.immediate

TrackingView:
- .onChange(of: tracker.isTracking) → Start/End
- persistTicker (5s) → update
- .onChange(of: tracker.isPaused/isAutoPaused) → sofort update für saubere UX

BanYaroGo-Info.plist: NSSupportsLiveActivities = true

Shared/WalkActivityAttributes.swift

@@ -0,0 +1,38 @@
+import Foundation
+import ActivityKit
+
+/// Live Activity attributes for a running Gassi-Tour. Lives in `Shared/` and
+/// is compiled into both the app target (which starts/updates/ends activities)
+/// and the widget extension (which renders the lock screen + Dynamic Island).
+struct WalkActivityAttributes: ActivityAttributes {
+    public typealias ContentState = WalkActivityState
+
+    public struct WalkActivityState: Codable, Hashable {
+        public var distanceMeters: Double
+        public var elapsedSeconds: Int
+        public var pointCount: Int
+        public var isPaused: Bool
+        public var isAutoPaused: Bool
+
+        public init(
+            distanceMeters: Double,
+            elapsedSeconds: Int,
+            pointCount: Int,
+            isPaused: Bool,
+            isAutoPaused: Bool
+        ) {
+            self.distanceMeters = distanceMeters
+            self.elapsedSeconds = elapsedSeconds
+            self.pointCount = pointCount
+            self.isPaused = isPaused
+            self.isAutoPaused = isAutoPaused
+        }
+    }
+
+    /// Walk start time — fixed for the duration of the activity.
+    public var startedAt: Date
+
+    public init(startedAt: Date) {
+        self.startedAt = startedAt
+    }
+}