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/core/src/types.ts

@@ -148,11 +148,11 @@ export interface Task {
   validatorModelId?: string;
   /** Number of merge retry attempts made for this task (auto-merge conflict recovery) */
   mergeRetries?: number;
-  /** Error message from the last failure, if the task failed during execution */
-  error?: string;
   /** ISO-8601 timestamp of when the task last entered its current column.
    *  Used to sort cards within a column so that recently-moved cards appear at the top. */
   columnMovedAt?: string;
+  /** Error message from the last failure, if the task failed during execution */
+  error?: string;
   createdAt: string;
   updatedAt: string;
 }