feat(backend/WebApp): implement content safety and filter handling

Added content safety analysis and prompt injection detection features to the agent streaming service. Introduced handling for content filter
exceptions and integrated SSE events for real-time feedback on content filter violations. Updated the agent controller and streaming service
to manage content filter responses and maintain conversation continuity.

Modified files (12):
- TaskAgent.Application/Interfaces/IAgentStreamingService.cs: Added method for content filter exception retrieval
- TaskAgent.Application/Interfaces/IContentSafetyService.cs: Removed interface for content safety service
- TaskAgent.Infrastructure/Services/AgentStreamingService.cs: Implemented content filter handling and exception management
- TaskAgent.WebApi/Controllers/AgentController.cs: Updated to handle content filter events and responses
- TaskAgent.WebApi/Services/SseStreamingService.cs: Added content filter event sending logic
- TaskAgent.WebApi/Constants/AgentConstants.cs: Defined constants for content filter events and messages
- TaskAgent.Application/DTOs/ContentSafetyResult.cs: Removed DTO for content safety results
- TaskAgent.Application/DTOs/PromptInjectionResult.cs: Removed DTO for prompt injection results
- TaskAgent.Infrastructure/Constants/ContentSafetyConstants.cs: Removed constants related to content safety
- TaskAgent.Infrastructure/Models/ContentSafetyConfig.cs: Removed model for content safety configuration
- TaskAgent.Infrastructure/Models/PromptShieldResponse.cs: Removed model for prompt shield response
- TaskAgent.Infrastructure/Services/ContentSafetyService.cs: Removed content safety service implementation

Author: cristofima

src/backend/services/TaskAgent/src/TaskAgent.Application/DTOs/ContentSafetyResult.cs

@@ -41,4 +41,10 @@ IAsyncEnumerable<object> StreamResponseAsync(
     /// <param name="serializedState">Serialized thread state.</param>
     /// <returns>Deserialized agent thread or new thread if deserialization fails.</returns>
     object DeserializeThread(string? serializedState);
+
+    /// <summary>
+    /// Gets the content filter exception if one occurred during the last streaming operation.
+    /// </summary>
+    /// <returns>ContentFilterException if content was filtered, null otherwise.</returns>
+    object? GetContentFilterException();
 }

src/backend/services/TaskAgent/src/TaskAgent.Application/DTOs/PromptInjectionResult.cs

@@ -1,5 +1,3 @@
-using Azure;
-using Azure.AI.ContentSafety;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -55,47 +53,6 @@ IConfiguration configuration
         services.AddScoped<IAgentStreamingService, AgentStreamingService>();
         services.AddScoped<IConversationService, ConversationService>();
 
-        RegisterContentSafety(services, configuration);
-
         return services;
     }
-
-    /// <summary>
-    /// Register Azure Content Safety infrastructure
-    /// </summary>
-    private static void RegisterContentSafety(
-        IServiceCollection services,
-        IConfiguration configuration
-    )
-    {
-        string? contentSafetyEndpoint = configuration["ContentSafety:Endpoint"];
-        string? contentSafetyApiKey = configuration["ContentSafety:ApiKey"];
-
-        if (
-            string.IsNullOrWhiteSpace(contentSafetyEndpoint)
-            || string.IsNullOrWhiteSpace(contentSafetyApiKey)
-        )
-        {
-            throw new InvalidOperationException(
-                "Content Safety configuration is required. Please configure ContentSafety:Endpoint and ContentSafety:ApiKey."
-            );
-        }
-
-        var contentSafetyClient = new ContentSafetyClient(
-            new Uri(contentSafetyEndpoint),
-            new AzureKeyCredential(contentSafetyApiKey)
-        );
-        services.AddSingleton(contentSafetyClient);
-
-        services.AddHttpClient(
-            "ContentSafety",
-            client =>
-            {
-                client.BaseAddress = new Uri(contentSafetyEndpoint);
-                client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", contentSafetyApiKey);
-            }
-        );
-
-        services.AddScoped<IContentSafetyService, ContentSafetyService>();
-    }
 }