Add a new helper `getTopLevelTaskList` that excludes sub-tasks (tasks whose parent is another task) from the flat task list. This changes both `matchRuleIds` and `getViewItems` to iterate only over top-level tasks, ensuring Inbox, Today, Scheduled, and Completed views never accidentally surface implementation-detail sub-tasks as first-class matches.

Previously, sub-tasks were present in all cross-cutting lists. They are now correctly hidden because they are internal to their parent and should not appear in global views or search results.