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" : ""}`}

packages/dashboard/app/styles.css

@@ -512,30 +512,6 @@ body {
   border-left: 3px solid #da3633;
 }
 
-/* Error display on failed task cards */
-.card-error {
-  display: flex;
-  align-items: flex-start;
-  gap: 6px;
-  margin: 6px 0;
-  padding: 6px 8px;
-  background: rgba(218, 54, 51, 0.1);
-  border: 1px solid rgba(218, 54, 51, 0.3);
-  border-radius: var(--radius);
-  font-size: 11px;
-  color: #da3633;
-  line-height: 1.4;
-}
-
-.card-error-icon {
-  flex-shrink: 0;
-  font-size: 12px;
-}
-
-.card-error-text {
-  word-break: break-word;
-}
-
 .card.paused {
   opacity: 0.55;
   border-left: 3px solid var(--text-secondary, #888);
@@ -1104,43 +1080,6 @@ body {
   margin-bottom: 16px;
 }
 
-/* Error alert in task detail modal */
-.detail-error-alert {
-  display: flex;
-  align-items: flex-start;
-  gap: 12px;
-  margin: 12px 0 16px;
-  padding: 12px 14px;
-  background: rgba(218, 54, 51, 0.1);
-  border: 1px solid rgba(218, 54, 51, 0.3);
-  border-radius: var(--radius);
-}
-
-.detail-error-icon {
-  flex-shrink: 0;
-  font-size: 18px;
-  line-height: 1;
-}
-
-.detail-error-content {
-  flex: 1;
-  min-width: 0;
-}
-
-.detail-error-title {
-  font-size: 13px;
-  font-weight: 600;
-  color: #da3633;
-  margin-bottom: 4px;
-}
-
-.detail-error-message {
-  font-size: 12px;
-  color: var(--text-muted);
-  line-height: 1.5;
-  word-break: break-word;
-}
-
 .detail-section {
   margin-top: 16px;
 }