Initial implementation of Fantasy Hockey watchOS app

Implemented complete TCA architecture for iOS and watchOS targets:
- Authentication flow (Sign in with Apple + Yahoo OAuth)
- OAuth token management with iCloud Key-Value Storage
- Yahoo Fantasy Sports API client with async/await
- Watch Connectivity for iPhone ↔ Watch data sync
- Complete UI for both iPhone and Watch platforms

Core features:
- Matchup score display
- Category breakdown with win/loss/tie indicators
- Roster status tracking
- Manual refresh functionality
- Persistent data caching on Watch

Technical stack:
- The Composable Architecture for state management
- Swift Concurrency (async/await, actors)
- WatchConnectivity framework
- Sign in with Apple
- OAuth 2.0 authentication flow

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

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

FantasyWatch/Shared/Networking/OAuth/OAuthManager.swift

@@ -0,0 +1,110 @@
+//
+//  OAuthManager.swift
+//  FantasyWatch
+//
+//  Created by Claude Code
+//
+
+import Foundation
+
+actor OAuthManager {
+    private let tokenStorage: OAuthTokenStorage
+    private let clientID: String
+    private let clientSecret: String
+    private var refreshTask: Task<TokenPair, Error>?
+    private var currentUserID: String?
+
+    init(
+        tokenStorage: OAuthTokenStorage,
+        clientID: String,
+        clientSecret: String
+    ) {
+        self.tokenStorage = tokenStorage
+        self.clientID = clientID
+        self.clientSecret = clientSecret
+    }
+
+    func setCurrentUser(_ userID: String) {
+        self.currentUserID = userID
+    }
+
+    func validToken() async throws -> String {
+        guard let userID = currentUserID else {
+            throw OAuthError.authorizationFailed
+        }
+
+        if await tokenStorage.isTokenValid(for: userID) {
+            guard let token = await tokenStorage.getAccessToken(for: userID) else {
+                throw OAuthError.tokenExpired
+            }
+            return token
+        }
+
+        let refreshedTokenPair = try await refreshToken()
+        return refreshedTokenPair.accessToken
+    }
+
+    func refreshToken() async throws -> TokenPair {
+        if let existingTask = refreshTask {
+            return try await existingTask.value
+        }
+
+        guard let userID = currentUserID else {
+            throw OAuthError.authorizationFailed
+        }
+
+        guard let refreshToken = await tokenStorage.getRefreshToken(for: userID) else {
+            throw OAuthError.noRefreshToken
+        }
+
+        let task = Task<TokenPair, Error> {
+            let url = URL(string: "https://api.login.yahoo.com/oauth2/get_token")!
+            var request = URLRequest(url: url)
+            request.httpMethod = "POST"
+            request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
+
+            let bodyParams = [
+                "grant_type": "refresh_token",
+                "refresh_token": refreshToken,
+                "client_id": clientID,
+                "client_secret": clientSecret
+            ]
+
+            let bodyString = bodyParams
+                .map { "\($0.key)=\($0.value)" }
+                .joined(separator: "&")
+
+            request.httpBody = bodyString.data(using: .utf8)
+
+            let (data, response) = try await URLSession.shared.data(for: request)
+
+            guard let httpResponse = response as? HTTPURLResponse,
+                  (200...299).contains(httpResponse.statusCode) else {
+                throw OAuthError.invalidResponse
+            }
+
+            let tokenResponse = try JSONDecoder().decode(OAuthTokenResponse.self, from: data)
+            let tokenPair = tokenResponse.toTokenPair()
+
+            await tokenStorage.saveTokenPair(tokenPair, for: userID)
+
+            return tokenPair
+        }
+
+        refreshTask = task
+
+        defer { refreshTask = nil }
+
+        return try await task.value
+    }
+
+    func saveTokenPair(_ tokenPair: TokenPair) async {
+        guard let userID = currentUserID else { return }
+        await tokenStorage.saveTokenPair(tokenPair, for: userID)
+    }
+
+    func clearTokens() async {
+        guard let userID = currentUserID else { return }
+        await tokenStorage.clearTokens(for: userID)
+    }
+}