feat(web): add real-time activity feed via SignalR

- Add ActivityHub and wire up SignalR in Program.cs
- Broadcast new context events from ContextController
- Connect SignalR client on Analytics page for live feed updates
- Restructure activity feed HTML to support live prepending
- Add slide-in animation for new activity items
- Update CORS to allow credentials for SignalR

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

TaskTracker.Api/Controllers/ContextController.cs

@@ -1,4 +1,6 @@
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.SignalR;
+using TaskTracker.Api.Hubs;
 using TaskTracker.Core.DTOs;
 using TaskTracker.Core.Entities;
 using TaskTracker.Core.Interfaces;
@@ -11,6 +13,7 @@ public class ContextController(
     IContextEventRepository contextRepo,
     IAppMappingRepository mappingRepo,
     ITaskRepository taskRepo,
+    IHubContext<ActivityHub> hubContext,
     ILogger<ContextController> logger) : ControllerBase
 {
     [HttpPost]
@@ -37,6 +40,17 @@ public class ContextController(
         }
 
         var created = await contextRepo.CreateAsync(contextEvent);
+
+        await hubContext.Clients.All.SendAsync("NewActivity", new
+        {
+            id = created.Id,
+            appName = created.AppName,
+            windowTitle = created.WindowTitle,
+            url = created.Url,
+            timestamp = created.Timestamp,
+            workTaskId = created.WorkTaskId
+        });
+
         return Ok(ApiResponse<ContextEvent>.Ok(created));
     }