Workouts 2.0: re-base persistence on iCloud Drive documents

Replace Core Data + NSPersistentCloudKitContainer + App-Group store +
WatchConnectivity dictionary sync with the QuickRabbit iCloud-documents
architecture:

- iCloud Drive JSON documents are the sole source of truth (one file per
  aggregate: Splits/<ULID>.json, Workouts/YYYY/MM/<ULID>.json), with a
  rebuildable SwiftData cache populated only by an NSMetadataQuery observer
  and a connect-time reconcile. Soft-delete tombstones; hard iCloud gate.
- Shared model layer (ULID, Codable *Documents + stateless mappers, @Model
  cache entities, SwiftData container) compiled into both targets.
- New iPhone<->Watch bridge over WatchConnectivity keyed by ULIDs; the phone
  is the sole writer of iCloud Drive, the watch round-trips documents.
- AppServices DI + iCloud-required root gate; Swift 6 strict concurrency.
- Starter splits generated on demand from the bundled YAML catalogs.
- Migrate to XcodeGen (project.yml), iOS 26 / watchOS 26; CloudDocuments
  entitlement (drop CloudKit/App Group/aps-environment).
- Duration stored as Int seconds (was a Date epoch hack); fix workout
  end-on-create, undismissable delete dialog, toolbar-hiding nav stacks,
  and the Settings placeholder.
- Add README/CHANGELOG/LICENSE, .gitignore, refreshed REQUIREMENTS, and the
  Scripts/ TestFlight pipeline (release.sh + ASC API scripts).

MARKETING_VERSION 2.0.

Workouts/Views/RootGateView.swift

@@ -0,0 +1,33 @@
+import SwiftUI
+
+/// Gates the whole UI on iCloud availability. Files are the source of truth, so
+/// there is no meaningful app without iCloud — we never fall back to local-only.
+struct RootGateView: View {
+    @Environment(SyncEngine.self) private var syncEngine
+    @Environment(\.scenePhase) private var scenePhase
+
+    var body: some View {
+        Group {
+            switch syncEngine.iCloudStatus {
+            case .checking:
+                ProgressView("Connecting to iCloud…")
+            case .available:
+                ContentView()
+            case .unavailable:
+                ContentUnavailableView {
+                    Label("iCloud Required", systemImage: "icloud.slash")
+                } description: {
+                    Text("Sign in to iCloud in Settings to use Workouts. Your data lives in iCloud Drive so it's safe and on all your devices.")
+                } actions: {
+                    Button("Try Again") { Task { await syncEngine.connect() } }
+                        .buttonStyle(.borderedProminent)
+                }
+            }
+        }
+        .onChange(of: scenePhase) { _, phase in
+            if phase == .active, syncEngine.iCloudStatus == .unavailable {
+                Task { await syncEngine.connect() }
+            }
+        }
+    }
+}