feat: add EstimatedMinutes field and general PUT update endpoint for tasks

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

TaskTracker.Infrastructure/Migrations/TaskTrackerDbContextModelSnapshot.cs

@@ -189,6 +189,9 @@ namespace TaskTracker.Infrastructure.Migrations
                     b.Property<string>("Description")
                         .HasColumnType("nvarchar(max)");
 
+                    b.Property<int?>("EstimatedMinutes")
+                        .HasColumnType("int");
+
                     b.Property<int?>("ParentTaskId")
                         .HasColumnType("int");