refactor: separate Nakama provider concerns into context, refs, and state modules

- Extracted context contract to `contexts.ts` (NakamaContextType)
- Added strongly typed internal provider refs in `refs.ts`
  - socketRef: React.RefObject<Socket | null>
  - gameMetadataRef: React.RefObject<GameMetadata | null>
- Added `NakamaProviderState` in `states.ts` for React-managed provider state
  - session, socket, matchId, matchmakerTicket
- Refactored NakamaProvider to use new modular structure
  - Replaced scattered useState/useRef with structured internal state + refs
  - Updated onMatchData to use MatchDataMessage model
  - Replaced deprecated MutableRefObject typing with RefObject
  - Cleaned update patterns using `updateState` helper
- Updated imports to use new models and context structure
- Improved separation of responsibilities:
  - models = pure domain types
  - context = exposed provider API
  - refs = internal mutable runtime refs
  - state = provider-managed reactive state
- Ensured all Nakama provider functions fully typed and consistent with TS

This refactor improves clarity, type safety, and maintainability for the
Nakama real-time multiplayer provider.

src/App.tsx

@@ -2,7 +2,7 @@ import React, { useState, useEffect } from "react";
 import { motion } from "framer-motion";
 import { useNakama } from "./providers/NakamaProvider";
 import Player from "./Player";
-import { PlayerModel } from "./models/player";
+import { PlayerModel } from "./interfaces/models";
 
 import TicTacToeBoard from "./games/tictactoe/TicTacToeBoard";
 import BattleShipBoard from "./games/battleship/BattleShipBoard";