feat(itinerary): add draggable travel day positioning with CloudKit persistence

- Add TravelDayOverride model for storing user-customized travel day positions
- Add TravelOverrideService for CloudKit CRUD operations on travel overrides
- Add CKTravelDayOverride CloudKit model wrapper
- Refactor itinerarySections to validate travel day bounds (must be after last game in departure city)
- Travel segments can now be dragged to different days within valid range
- Persist travel day overrides to CloudKit for cross-device sync

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

SportsTime/Core/Models/CloudKit/CKModels.swift

@@ -21,6 +21,7 @@ enum CKRecordType {
     static let tripPoll = "TripPoll"
     static let pollVote = "PollVote"
     static let customItineraryItem = "CustomItineraryItem"
+    static let travelDayOverride = "TravelDayOverride"
 }
 
 // MARK: - CKTeam
@@ -694,3 +695,55 @@ struct CKCustomItineraryItem {
         )
     }
 }
+
+// MARK: - CKTravelDayOverride
+
+struct CKTravelDayOverride {
+    static let overrideIdKey = "overrideId"
+    static let tripIdKey = "tripId"
+    static let travelAnchorIdKey = "travelAnchorId"
+    static let displayDayKey = "displayDay"
+    static let createdAtKey = "createdAt"
+    static let modifiedAtKey = "modifiedAt"
+
+    let record: CKRecord
+
+    init(record: CKRecord) {
+        self.record = record
+    }
+
+    init(override: TravelDayOverride) {
+        let record = CKRecord(
+            recordType: CKRecordType.travelDayOverride,
+            recordID: CKRecord.ID(recordName: override.id.uuidString)
+        )
+        record[CKTravelDayOverride.overrideIdKey] = override.id.uuidString
+        record[CKTravelDayOverride.tripIdKey] = override.tripId.uuidString
+        record[CKTravelDayOverride.travelAnchorIdKey] = override.travelAnchorId
+        record[CKTravelDayOverride.displayDayKey] = override.displayDay
+        record[CKTravelDayOverride.createdAtKey] = override.createdAt
+        record[CKTravelDayOverride.modifiedAtKey] = override.modifiedAt
+        self.record = record
+    }
+
+    func toOverride() -> TravelDayOverride? {
+        guard let overrideIdString = record[CKTravelDayOverride.overrideIdKey] as? String,
+              let overrideId = UUID(uuidString: overrideIdString),
+              let tripIdString = record[CKTravelDayOverride.tripIdKey] as? String,
+              let tripId = UUID(uuidString: tripIdString),
+              let travelAnchorId = record[CKTravelDayOverride.travelAnchorIdKey] as? String,
+              let displayDay = record[CKTravelDayOverride.displayDayKey] as? Int,
+              let createdAt = record[CKTravelDayOverride.createdAtKey] as? Date,
+              let modifiedAt = record[CKTravelDayOverride.modifiedAtKey] as? Date
+        else { return nil }
+
+        return TravelDayOverride(
+            id: overrideId,
+            tripId: tripId,
+            travelAnchorId: travelAnchorId,
+            displayDay: displayDay,
+            createdAt: createdAt,
+            modifiedAt: modifiedAt
+        )
+    }
+}