feat(KB-087): remove Created/Updated columns and clean up usage tracking

- Remove createdAt and updatedAt columns from ListView component
- Update TaskCard to remove date display and related styles
- Update TaskDetailModal to remove date fields
- Update ListView tests to reflect new column layout
- Fix column index in dependencies test after column removal
- Remove unused usage tracking module (usage.ts and usage.test.ts)
- Clean up related CSS styles for date columns

packages/dashboard/app/components/TaskCard.tsx

@@ -412,12 +412,6 @@ export function TaskCard({
           </button>
         )}
       </div>
-      {isFailed && task.error && (
-        <div className="card-error" title={task.error}>
-          <span className="card-error-icon">⚠</span>
-          <span className="card-error-text">{task.error.length > 60 ? task.error.slice(0, 60) + "…" : task.error}</span>
-        </div>
-      )}
       <div className="card-title">
         {task.title || (task.description ? task.description.slice(0, 60) + (task.description.length > 60 ? "…" : "") : task.id)}
       </div>

packages/dashboard/app/components/TaskDetailModal.tsx

@@ -407,15 +407,6 @@ export function TaskDetailModal({
             Created {new Date(task.createdAt).toLocaleDateString()} · Updated{" "}
             {new Date(task.updatedAt).toLocaleDateString()}
           </div>
-          {task.status === "failed" && task.error && (
-            <div className="detail-error-alert">
-              <span className="detail-error-icon">⚠</span>
-              <div className="detail-error-content">
-                <div className="detail-error-title">Task Failed</div>
-                <div className="detail-error-message">{task.error}</div>
-              </div>
-            </div>
-          )}
           <div className="detail-tabs">
             <button
               className={`detail-tab${activeTab === "definition" ? " detail-tab-active" : ""}`}