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/Info.plist

@@ -5,6 +5,8 @@
 	<key>UIBackgroundModes</key>
 	<array>
 		<string>remote-notification</string>
+		<string>fetch</string>
+		<string>processing</string>
 	</array>
 </dict>
 </plist>