Implement LLM provider configuration and update user settings

- Added functionality to update the default LLM provider for users via a new endpoint in UserController.
- Introduced LlmProvider enum to manage available LLM options: Auto, Gemini, OpenAI, and Claude.
- Updated User and UserEntity models to include DefaultLlmProvider property.
- Enhanced database context and migrations to support the new LLM provider configuration.
- Integrated LLM services into the application bootstrap for dependency injection.
- Updated TypeScript API client to include methods for managing LLM providers and chat requests.

src/Managing.Application/Users/UserService.cs

@@ -339,6 +339,22 @@ public class UserService : IUserService
         return user;
     }
 
+    public async Task<User> UpdateDefaultLlmProvider(User user, LlmProvider defaultLlmProvider)
+    {
+        user = await GetUserByName(user.Name);
+        if (user.DefaultLlmProvider == defaultLlmProvider)
+            return user;
+
+        // Update the default LLM provider on the provided user object
+        user.DefaultLlmProvider = defaultLlmProvider;
+        await _userRepository.SaveOrUpdateUserAsync(user);
+
+        _logger.LogInformation("Updated default LLM provider to {Provider} for user {UserId}", 
+            defaultLlmProvider, user.Id);
+
+        return user;
+    }
+
     public async Task<User> UpdateUserSettings(User user, UserSettingsDto settings)
     {
         user = await GetUserByName(user.Name);