feat(sync): add pagination, cancellation, and network restoration

- CloudKit pagination: fetchAllRecords() handles >400 record batches
  with cursor-based pagination (400 records per page)
- Cancellation support: SyncCancellationToken protocol enables graceful
  sync termination when background tasks expire
- Per-entity progress: SyncState now tracks timestamps per entity type
  so interrupted syncs resume where they left off
- NetworkMonitor: NWPathMonitor integration triggers sync on network
  restoration with 2.5s debounce to handle WiFi↔cellular flapping
- wasCancelled flag in SyncResult distinguishes partial from full syncs

This addresses critical data sync issues:
- CloudKit queries were limited to ~400 records but bundled data has ~5000 games
- Background tasks could be killed mid-sync without saving progress
- App had no awareness of network state changes

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

SportsTime/Core/Services/SyncCancellationToken.swift

@@ -0,0 +1,27 @@
+//
+//  SyncCancellationToken.swift
+//  SportsTime
+//
+//  Cancellation support for long-running sync operations.
+//
+
+import Foundation
+import os
+
+/// Protocol for cancellation tokens checked between sync pages
+protocol SyncCancellationToken: Sendable {
+    var isCancelled: Bool { get }
+}
+
+/// Concrete cancellation token for background tasks
+final class BackgroundTaskCancellationToken: SyncCancellationToken, @unchecked Sendable {
+    private let lock = OSAllocatedUnfairLock(initialState: false)
+
+    var isCancelled: Bool {
+        lock.withLock { $0 }
+    }
+
+    func cancel() {
+        lock.withLock { $0 = true }
+    }
+}