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/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;
 }