Run AI classification in background with SignalR notifications

Move the classify-uncategorized endpoint from synchronous to async.
The controller now queues a ClassificationJob to an unbounded channel
and returns 202 Accepted. A new BackgroundService processes jobs and
pushes results (or errors) to the user via SignalR. The frontend
listens for the AiClassificationComplete event and surfaces it in the
notification system.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/Purrse.Api/Controllers/AiCategorizationController.cs

@@ -1,5 +1,7 @@
+using System.Threading.Channels;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using Purrse.Api.Services;
 using Purrse.Core.DTOs;
 using Purrse.Core.Interfaces.Services;
 using System.Security.Claims;
@@ -12,9 +14,14 @@ namespace Purrse.Api.Controllers;
 public class AiCategorizationController : ControllerBase
 {
     private readonly IAiCategorizationService _aiService;
+    private readonly Channel<ClassificationJob> _classificationChannel;
     private Guid UserId => Guid.Parse(User.FindFirstValue(ClaimTypes.NameIdentifier)!);
 
-    public AiCategorizationController(IAiCategorizationService aiService) => _aiService = aiService;
+    public AiCategorizationController(IAiCategorizationService aiService, Channel<ClassificationJob> classificationChannel)
+    {
+        _aiService = aiService;
+        _classificationChannel = classificationChannel;
+    }
 
     [HttpGet("settings")]
     public async Task<ActionResult<AiCategorizationSettingsResponse>> GetSettings()
@@ -29,6 +36,10 @@ public class AiCategorizationController : ControllerBase
         => Ok(await _aiService.TestConnectionAsync(UserId));
 
     [HttpPost("classify")]
-    public async Task<ActionResult<ClassifyUncategorizedResponse>> ClassifyUncategorized(ClassifyUncategorizedRequest request)
-        => Ok(await _aiService.ClassifyUncategorizedAsync(UserId, request));
+    public async Task<IActionResult> ClassifyUncategorized(ClassifyUncategorizedRequest request)
+    {
+        var job = new ClassificationJob(UserId, request.AccountId, request.StartDate, request.EndDate, request.SearchText, request.Status);
+        await _classificationChannel.Writer.WriteAsync(job);
+        return Accepted(new { message = "Classification job queued" });
+    }
 }