refactor: change domain model IDs from UUID to String canonical IDs

This refactor fixes the achievement system by using stable canonical string
IDs (e.g., "stadium_mlb_fenway_park") instead of random UUIDs. This ensures
stadium mappings for achievements are consistent across app launches and
CloudKit sync operations.

Changes:
- Stadium, Team, Game: id property changed from UUID to String
- Trip, TripStop, TripPreferences: updated to use String IDs for games/stadiums
- CKModels: removed UUID parsing, use canonical IDs directly
- AchievementEngine: now matches against canonical stadium IDs
- All test files updated to use String IDs instead of UUID()

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

SportsTimeTests/Planning/ConcurrencyTests.swift

@@ -30,7 +30,7 @@ struct ConcurrencyTests {
 
     /// Creates a stadium at a known location
     private func makeStadium(
-        id: UUID = UUID(),
+        id: String = "stadium_test_\(UUID().uuidString)",
         city: String,
         lat: Double,
         lon: Double,
@@ -50,10 +50,10 @@ struct ConcurrencyTests {
 
     /// Creates a game at a stadium
     private func makeGame(
-        id: UUID = UUID(),
-        stadiumId: UUID,
-        homeTeamId: UUID = UUID(),
-        awayTeamId: UUID = UUID(),
+        id: String = "game_test_\(UUID().uuidString)",
+        stadiumId: String,
+        homeTeamId: String = "team_test_\(UUID().uuidString)",
+        awayTeamId: String = "team_test_\(UUID().uuidString)",
         dateTime: Date,
         sport: Sport = .mlb
     ) -> Game {
@@ -73,7 +73,7 @@ struct ConcurrencyTests {
         startDate: Date,
         endDate: Date,
         games: [Game],
-        stadiums: [UUID: Stadium]
+        stadiums: [String: Stadium]
     ) -> PlanningRequest {
         let preferences = TripPreferences(
             planningMode: .dateRange,
@@ -107,8 +107,8 @@ struct ConcurrencyTests {
 
         let pair = cityPairs[requestIndex % cityPairs.count]
 
-        let stadium1Id = UUID()
-        let stadium2Id = UUID()
+        let stadium1Id = "stadium_1_\(UUID().uuidString)"
+        let stadium2Id = "stadium_2_\(UUID().uuidString)"
 
         let stadium1 = makeStadium(id: stadium1Id, city: pair.city1.0, lat: pair.city1.1, lon: pair.city1.2)
         let stadium2 = makeStadium(id: stadium2Id, city: pair.city2.0, lat: pair.city2.1, lon: pair.city2.2)