Add StadiumAlias CloudKit sync and offline-first data architecture

- Add CKStadiumAlias model for CloudKit record mapping
- Add fetchStadiumAliases/fetchStadiumAliasChanges to CloudKitService
- Add syncStadiumAliases to CanonicalSyncService for delta sync
- Add subscribeToStadiumAliasUpdates for push notifications
- Update cloudkit_import.py with --stadium-aliases-only option

Data Architecture Updates:
- Remove obsolete provider files (CanonicalDataProvider, CloudKitDataProvider, StubDataProvider)
- AppDataProvider now reads exclusively from SwiftData
- Add background CloudKit sync on app startup (non-blocking)
- Document data architecture in CLAUDE.md

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

CLAUDE.md

@@ -50,11 +50,75 @@ This is an iOS app for planning multi-stop sports road trips. It uses **Clean MV
    - `Services/POISearchService` - Finds nearby restaurants, attractions via MKLocalSearch
    - `Services/PDFAssetPrefetcher` - Parallel prefetching of all PDF assets
 
-### Data Storage Strategy
+### Data Architecture (Offline-First)
 
-- **CloudKit Public DB**: Read-only schedules, stadiums, teams (shared across all users)
-- **SwiftData Local**: User's saved trips, preferences, cached schedules
-- **No network dependency** for trip planning once schedules are synced
+**CRITICAL: `AppDataProvider.shared` is the ONLY source of truth for canonical data.**
+
+All code that reads stadiums, teams, games, or league structure MUST use `AppDataProvider.shared`. Never access CloudKit or SwiftData directly for this data.
+
+```
+┌──────────────────┐     ┌──────────────────┐     ┌──────────────────┐
+│  Bundled JSON    │     │    SwiftData     │     │    CloudKit      │
+│  (App Bundle)    │     │  (Local Store)   │     │  (Remote Sync)   │
+└────────┬─────────┘     └────────▲─────────┘     └────────┬─────────┘
+         │                        │                        │
+         │ Bootstrap              │ Read                   │ Background
+         │ (first launch)        │                        │ Sync
+         ▼                        │                        ▼
+┌─────────────────────────────────┴────────────────────────────────────┐
+│                        AppDataProvider.shared                         │
+│                     (Single Source of Truth)                          │
+└─────────────────────────────────┬────────────────────────────────────┘
+                                  │
+                                  ▼
+                    All Features, ViewModels, Services
+```
+
+**App Startup Flow:**
+1. **Bootstrap** (first launch only): `BootstrapService` loads bundled JSON → SwiftData
+2. **Configure**: `AppDataProvider.shared.configure(with: context)`
+3. **Load**: `AppDataProvider.shared.loadInitialData()` reads SwiftData into memory
+4. **App usable immediately** with local data
+5. **Background sync**: `CanonicalSyncService.syncAll()` fetches CloudKit → updates SwiftData (non-blocking)
+6. **Reload**: After sync completes, `loadInitialData()` refreshes in-memory cache
+
+**Offline Handling:**
+- SwiftData always has data (from bootstrap or last successful CloudKit sync)
+- If CloudKit unavailable, app continues with existing local data
+- First launch + offline = bootstrap data used
+
+**Canonical Data Models** (in SwiftData, synced from CloudKit):
+- `CanonicalStadium` → `Stadium` (domain)
+- `CanonicalTeam` → `Team` (domain)
+- `CanonicalGame` → `Game` (domain)
+- `LeagueStructureModel`
+- `TeamAlias`, `StadiumAlias`
+
+**User Data Models** (local only, not synced):
+- `SavedTrip`, `StadiumVisit`, `UserPreferences`, `Achievement`
+
+**Correct Usage:**
+```swift
+// ✅ CORRECT - Use AppDataProvider
+let stadiums = AppDataProvider.shared.stadiums
+let teams = AppDataProvider.shared.teams
+let games = try await AppDataProvider.shared.fetchGames(sports: sports, startDate: start, endDate: end)
+let richGames = try await AppDataProvider.shared.fetchRichGames(...)
+
+// ❌ WRONG - Never access CloudKit directly for reads
+let stadiums = try await CloudKitService.shared.fetchStadiums() // NO!
+
+// ❌ WRONG - Never fetch canonical data from SwiftData directly
+let descriptor = FetchDescriptor<CanonicalStadium>()
+let stadiums = try context.fetch(descriptor) // NO! (except in DataProvider/Sync/Bootstrap)
+```
+
+**Allowed Direct SwiftData Access:**
+- `DataProvider.swift` - It IS the data provider
+- `CanonicalSyncService.swift` - CloudKit → SwiftData sync
+- `BootstrapService.swift` - Initial data population
+- `StadiumIdentityService.swift` - Specialized identity resolution for stadium renames
+- User data (e.g., `StadiumVisit`) - Not canonical data
 
 ### Key Data Flow