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/Mocks/MockAppDataProvider.swift

@@ -24,10 +24,10 @@ final class MockAppDataProvider: ObservableObject {
 
     // MARK: - Internal Storage
 
-    private var teamsById: [UUID: Team] = [:]
-    private var stadiumsById: [UUID: Stadium] = [:]
+    private var teamsById: [String: Team] = [:]
+    private var stadiumsById: [String: Stadium] = [:]
     private var games: [Game] = []
-    private var gamesById: [UUID: Game] = [:]
+    private var gamesById: [String: Game] = [:]
 
     // MARK: - Configuration
 
@@ -140,11 +140,11 @@ final class MockAppDataProvider: ObservableObject {
 
     // MARK: - Data Access
 
-    func team(for id: UUID) -> Team? {
+    func team(for id: String) -> Team? {
         teamsById[id]
     }
 
-    func stadium(for id: UUID) -> Stadium? {
+    func stadium(for id: String) -> Stadium? {
         stadiumsById[id]
     }
 
@@ -169,7 +169,7 @@ final class MockAppDataProvider: ObservableObject {
         }.sorted { $0.dateTime < $1.dateTime }
     }
 
-    func fetchGame(by id: UUID) async throws -> Game? {
+    func fetchGame(by id: String) async throws -> Game? {
         await simulateLatency()
 
         if config.shouldFailOnFetch {