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>

SportsTime/Planning/Models/PlanningModels.swift

@@ -251,7 +251,7 @@ struct ItineraryStop: Identifiable, Hashable {
     let city: String
     let state: String
     let coordinate: CLLocationCoordinate2D?
-    let games: [UUID]
+    let games: [String]  // Canonical game IDs
     let arrivalDate: Date
     let departureDate: Date
     let location: LocationInput
@@ -490,8 +490,8 @@ extension ItineraryOption {
 struct PlanningRequest {
     let preferences: TripPreferences
     let availableGames: [Game]
-    let teams: [UUID: Team]
-    let stadiums: [UUID: Stadium]
+    let teams: [String: Team]      // Keyed by canonical ID
+    let stadiums: [String: Stadium]  // Keyed by canonical ID
 
     // MARK: - Computed Properties for Engine