Refactor: Introduce Domain Services & Clean API Layer for Codele

[Copilot]

This PR introduces explicit domain services and DTO boundaries to decouple game logic from UI & hosting layers, enabling easier testing, future rule variants, and clearer API evolution.

Problem Statement

The existing Codele implementation had several architectural issues:

• Game-specific logic resided in the Blazor component (PlayCodele.razor) and API endpoints
• Internal game models (Guess, LetterStatus) were leaked directly via API responses
• Adding variants (hard mode, timed mode) would require branching conditionals throughout UI/API layers
• Game logic was tightly coupled to presentation concerns

Solution

Domain Layer Architecture

Introduced a clean domain layer in the CodeleLogic project with explicit interfaces:

• IWordProvider: Provides target words (current implementation uses in-memory coding-related words)
• IGuessEvaluator: Evaluates guesses against target words using existing Wordle logic
• GameSession: Aggregate that manages game state, attempts, and completion status
• IGameService: Orchestrates session creation and guess submission

API Layer Refactoring

Replaced direct logic endpoints with thin controllers that:

• Call IGameService for all game operations
• Return structured DTOs: GameSessionDto, GuessResultDto, LetterResultDto
• Handle domain exceptions with proper HTTP status codes (400/404/409)
• Maintain backward compatibility with legacy /codele-words endpoint

New endpoints:

POST /api/games              # Create new game session
GET /api/games/{gameId}      # Get current game state  
POST /api/games/{gameId}/guesses  # Submit a guess

Client Layer Updates

The Blazor client now:

• Uses only DTOs from the API (no direct domain dependencies)
• Implements async game operations with proper error handling
• Maintains identical user experience while being fully decoupled

Benefits Delivered

• Testability: 9 new unit tests covering all domain services and edge cases
• Extensibility: Easy to add game variants via dependency injection
• API Evolution: Clean contracts enable versioning without breaking changes
• Separation of Concerns: Game logic isolated from presentation and infrastructure

Example Usage

// Domain service injection
builder.Services.AddSingleton<IWordProvider, InMemoryWordProvider>();
builder.Services.AddSingleton<IGuessEvaluator, DefaultGuessEvaluator>();
builder.Services.AddSingleton<IGameService, DefaultGameService>();

// Clean API usage
var gameSession = await gameService.CreateGameSessionAsync();
var updatedSession = await gameService.SubmitGuessAsync(gameId, "apple");

All existing game functionality works unchanged from the user perspective, with comprehensive test coverage ensuring reliability.

Fixes #8.

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