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/Fixtures/FixtureGenerator.swift

@@ -68,8 +68,8 @@ struct FixtureGenerator {
         let stadiums: [Stadium]
         let teams: [Team]
         let games: [Game]
-        let stadiumsById: [UUID: Stadium]
-        let teamsById: [UUID: Team]
+        let stadiumsById: [String: Stadium]
+        let teamsById: [String: Team]
 
         func richGame(from game: Game) -> RichGame? {
             guard let homeTeam = teamsById[game.homeTeamId],
@@ -168,7 +168,7 @@ struct FixtureGenerator {
         return cities.enumerated().map { index, city in
             let sport = config.sports.randomElement(using: &rng) ?? .mlb
             return Stadium(
-                id: UUID(),
+                id: "stadium_test_\(city.name.lowercased().replacingOccurrences(of: " ", with: "_"))_\(index)",
                 name: "\(city.name) \(sport.rawValue) Stadium",
                 city: city.name,
                 state: city.state,
@@ -203,8 +203,9 @@ struct FixtureGenerator {
 
                 usedNames.insert("\(stadium.city) \(teamName)")
 
+                let teamId = "team_test_\(stadium.city.lowercased().replacingOccurrences(of: " ", with: "_"))_\(teamName.lowercased())_\(teams.count)"
                 teams.append(Team(
-                    id: UUID(),
+                    id: teamId,
                     name: teamName,
                     abbreviation: String(teamName.prefix(3)).uppercased(),
                     sport: stadium.sport,
@@ -251,8 +252,9 @@ struct FixtureGenerator {
             let hour = Int.random(in: 13...21, using: &rng)
             let gameDateTime = calendar.date(bySettingHour: hour, minute: 0, second: 0, of: gameDate)!
 
+            let gameId = "game_test_\(games.count)_\(homeTeam.abbreviation)_\(awayTeam.abbreviation)"
             games.append(Game(
-                id: UUID(),
+                id: gameId,
                 homeTeamId: homeTeam.id,
                 awayTeamId: awayTeam.id,
                 stadiumId: stadium.id,
@@ -331,8 +333,8 @@ struct FixtureGenerator {
                 coordinate: CLLocationCoordinate2D(latitude: city.lat, longitude: city.lon),
                 arrivalDate: currentDate,
                 departureDate: departureDate,
-                games: [UUID()],
-                stadium: UUID()
+                games: ["game_test_\(i)"],
+                stadium: "stadium_test_\(i)"
             ))
 
             currentDate = departureDate
@@ -351,12 +353,12 @@ struct FixtureGenerator {
         cities: [(name: String, lat: Double, lon: Double)],
         rng: inout SeededRandomNumberGenerator
     ) -> [Game] {
-        cities.map { city in
-            let stadiumId = UUID()
+        cities.enumerated().map { index, city in
+            let stadiumId = "stadium_conflict_\(city.name.lowercased().replacingOccurrences(of: " ", with: "_"))_\(index)"
             return Game(
-                id: UUID(),
-                homeTeamId: UUID(),
-                awayTeamId: UUID(),
+                id: "game_conflict_\(index)_\(city.name.lowercased().replacingOccurrences(of: " ", with: "_"))",
+                homeTeamId: "team_conflict_home_\(index)",
+                awayTeamId: "team_conflict_away_\(index)",
                 stadiumId: stadiumId,
                 dateTime: date,
                 sport: .mlb,
@@ -367,7 +369,7 @@ struct FixtureGenerator {
 
     /// Generate a stadium at a specific location
     static func makeStadium(
-        id: UUID = UUID(),
+        id: String = "stadium_test_\(UUID().uuidString)",
         name: String = "Test Stadium",
         city: String = "Test City",
         state: String = "TS",
@@ -390,12 +392,12 @@ struct FixtureGenerator {
 
     /// Generate a team
     static func makeTeam(
-        id: UUID = UUID(),
+        id: String = "team_test_\(UUID().uuidString)",
         name: String = "Test Team",
         abbreviation: String = "TST",
         sport: Sport = .mlb,
         city: String = "Test City",
-        stadiumId: UUID
+        stadiumId: String
     ) -> Team {
         Team(
             id: id,
@@ -409,10 +411,10 @@ struct FixtureGenerator {
 
     /// Generate a game
     static func makeGame(
-        id: UUID = UUID(),
-        homeTeamId: UUID,
-        awayTeamId: UUID,
-        stadiumId: UUID,
+        id: String = "game_test_\(UUID().uuidString)",
+        homeTeamId: String,
+        awayTeamId: String,
+        stadiumId: String,
         dateTime: Date = Date(),
         sport: Sport = .mlb,
         season: String = "2026",
@@ -454,8 +456,8 @@ struct FixtureGenerator {
         coordinate: CLLocationCoordinate2D? = nil,
         arrivalDate: Date = Date(),
         departureDate: Date? = nil,
-        games: [UUID] = [],
-        stadium: UUID? = nil,
+        games: [String] = [],
+        stadium: String? = nil,
         isRestDay: Bool = false
     ) -> TripStop {
         TripStop(