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/Core/Models/CloudKit/CKModels.swift

@@ -17,6 +17,7 @@ enum CKRecordType {
     static let sport = "Sport"
     static let leagueStructure = "LeagueStructure"
     static let teamAlias = "TeamAlias"
+    static let stadiumAlias = "StadiumAlias"
 }
 
 // MARK: - CKTeam
@@ -273,6 +274,55 @@ struct CKLeagueStructure {
     }
 }
 
+// MARK: - CKStadiumAlias
+
+struct CKStadiumAlias {
+    static let aliasNameKey = "aliasName"
+    static let stadiumCanonicalIdKey = "stadiumCanonicalId"
+    static let validFromKey = "validFrom"
+    static let validUntilKey = "validUntil"
+    static let schemaVersionKey = "schemaVersion"
+    static let lastModifiedKey = "lastModified"
+
+    let record: CKRecord
+
+    init(record: CKRecord) {
+        self.record = record
+    }
+
+    init(model: StadiumAlias) {
+        let record = CKRecord(recordType: CKRecordType.stadiumAlias, recordID: CKRecord.ID(recordName: model.aliasName))
+        record[CKStadiumAlias.aliasNameKey] = model.aliasName
+        record[CKStadiumAlias.stadiumCanonicalIdKey] = model.stadiumCanonicalId
+        record[CKStadiumAlias.validFromKey] = model.validFrom
+        record[CKStadiumAlias.validUntilKey] = model.validUntil
+        record[CKStadiumAlias.schemaVersionKey] = model.schemaVersion
+        record[CKStadiumAlias.lastModifiedKey] = model.lastModified
+        self.record = record
+    }
+
+    /// Convert to SwiftData model for local storage
+    func toModel() -> StadiumAlias? {
+        guard let aliasName = record[CKStadiumAlias.aliasNameKey] as? String,
+              let stadiumCanonicalId = record[CKStadiumAlias.stadiumCanonicalIdKey] as? String
+        else { return nil }
+
+        let validFrom = record[CKStadiumAlias.validFromKey] as? Date
+        let validUntil = record[CKStadiumAlias.validUntilKey] as? Date
+        let schemaVersion = record[CKStadiumAlias.schemaVersionKey] as? Int ?? SchemaVersion.current
+        let lastModified = record[CKStadiumAlias.lastModifiedKey] as? Date ?? record.modificationDate ?? Date()
+
+        return StadiumAlias(
+            aliasName: aliasName,
+            stadiumCanonicalId: stadiumCanonicalId,
+            validFrom: validFrom,
+            validUntil: validUntil,
+            schemaVersion: schemaVersion,
+            lastModified: lastModified
+        )
+    }
+}
+
 // MARK: - CKTeamAlias
 
 struct CKTeamAlias {