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/Program.cs

@@ -1,4 +1,5 @@
 using Microsoft.EntityFrameworkCore;
+using TaskTracker.Api.Hubs;
 using TaskTracker.Core.Interfaces;
 using TaskTracker.Infrastructure.Data;
 using TaskTracker.Infrastructure.Repositories;
@@ -31,12 +32,16 @@ builder.Services.AddCors(options =>
 {
     options.AddDefaultPolicy(policy =>
     {
-        policy.AllowAnyOrigin()
+        policy.SetIsOriginAllowed(_ => true)
               .AllowAnyHeader()
-              .AllowAnyMethod();
+              .AllowAnyMethod()
+              .AllowCredentials();
     });
 });
 
+// SignalR
+builder.Services.AddSignalR();
+
 // Razor Pages
 builder.Services.AddRazorPages();
 
@@ -57,5 +62,6 @@ app.UseCors();
 app.UseStaticFiles();
 app.MapRazorPages();
 app.MapControllers();
+app.MapHub<ActivityHub>("/hubs/activity");
 
 app.Run();