fix: resolve travel anchor ID collision for repeat city pairs

Include segment index in travel anchor IDs ("travel:INDEX:from->to")
so Follow Team trips visiting the same city pair multiple times get
unique, independently addressable travel segments. Prevents override
dictionary collisions and incorrect validDayRange lookups.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

SportsTime/Core/Models/Domain/ItineraryItem.swift

@@ -38,6 +38,7 @@ enum ItemKind: Codable, Hashable {
 struct TravelInfo: Codable, Hashable {
     let fromCity: String
     let toCity: String
+    var segmentIndex: Int? = nil  // Position in trip.travelSegments (nil for legacy records)
     var distanceMeters: Double?
     var durationSeconds: Double?
 

SportsTime/Core/Services/ItineraryItemService.swift

@@ -155,6 +155,7 @@ extension ItineraryItem {
             let info = TravelInfo(
                 fromCity: fromCity,
                 toCity: toCity,
+                segmentIndex: record["travelSegmentIndex"] as? Int,
                 distanceMeters: record["travelDistanceMeters"] as? Double,
                 durationSeconds: record["travelDurationSeconds"] as? Double
             )
@@ -198,6 +199,7 @@ extension ItineraryItem {
             record["kind"] = "travel"
             record["travelFromCity"] = info.fromCity
             record["travelToCity"] = info.toCity
+            record["travelSegmentIndex"] = info.segmentIndex
             record["travelDistanceMeters"] = info.distanceMeters
             record["travelDurationSeconds"] = info.durationSeconds