Add StadiumAlias CloudKit sync and offline-first data architecture

- Add CKStadiumAlias model for CloudKit record mapping
- Add fetchStadiumAliases/fetchStadiumAliasChanges to CloudKitService
- Add syncStadiumAliases to CanonicalSyncService for delta sync
- Add subscribeToStadiumAliasUpdates for push notifications
- Update cloudkit_import.py with --stadium-aliases-only option

Data Architecture Updates:
- Remove obsolete provider files (CanonicalDataProvider, CloudKitDataProvider, StubDataProvider)
- AppDataProvider now reads exclusively from SwiftData
- Add background CloudKit sync on app startup (non-blocking)
- Document data architecture in CLAUDE.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/SportsTimeApp.swift

@@ -90,13 +90,48 @@ struct BootstrappedContentView: View {
         let bootstrapService = BootstrapService()
 
         do {
+            // 1. Bootstrap from bundled JSON if first launch (no data exists)
             try await bootstrapService.bootstrapIfNeeded(context: context)
+
+            // 2. Configure DataProvider with SwiftData context
+            AppDataProvider.shared.configure(with: context)
+
+            // 3. Load data from SwiftData into memory
+            await AppDataProvider.shared.loadInitialData()
+
+            // 4. App is now usable
             isBootstrapping = false
+
+            // 5. Background: Try to refresh from CloudKit (non-blocking)
+            Task.detached(priority: .background) {
+                await self.performBackgroundSync(context: context)
+            }
         } catch {
             bootstrapError = error
             isBootstrapping = false
         }
     }
+
+    @MainActor
+    private func performBackgroundSync(context: ModelContext) async {
+        let syncService = CanonicalSyncService()
+
+        do {
+            let result = try await syncService.syncAll(context: context)
+
+            // If any data was updated, reload the DataProvider
+            if !result.isEmpty {
+                await AppDataProvider.shared.loadInitialData()
+                print("CloudKit sync completed: \(result.totalUpdated) items updated")
+            }
+        } catch CanonicalSyncService.SyncError.cloudKitUnavailable {
+            // Offline or CloudKit not available - silently continue with local data
+            print("CloudKit unavailable, using local data")
+        } catch {
+            // Other sync errors - log but don't interrupt user
+            print("Background sync error: \(error.localizedDescription)")
+        }
+    }
 }
 
 // MARK: - Bootstrap Loading View