feat: implement soft delete, task editing fixes, and UI improvements

Backend:
- Add soft delete for spaces and projects (is_active flag)
- Add status_id and assignee_id to TaskUpdate schema
- Fix task PATCH endpoint to update status and assignee
- Add validation for assignee_id and status_id in task updates
- Fix health service to count tasks with "Blocked" status as blockers
- Filter out deleted spaces/projects from health dashboard
- Add workload cache invalidation on assignee changes

Frontend:
- Add delete confirmation dialogs for spaces and projects
- Fix UserSelect to display selected user name (valueName prop)
- Fix task detail modal to refresh data after save
- Enforce 2-level subtask depth limit in UI
- Fix timezone bug in date formatting (use local timezone)
- Convert NotificationBell from Tailwind to inline styles
- Add i18n translations for health, workload, settings pages
- Add parent_task_id to Task interface across components

OpenSpec:
- Archive add-delete-capability change

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/services/workload_service.py

@@ -171,6 +171,7 @@ def get_workload_heatmap(
     week_start: Optional[date] = None,
     department_id: Optional[str] = None,
     user_ids: Optional[List[str]] = None,
+    hide_empty: bool = True,
 ) -> List[UserWorkloadSummary]:
     """
     Get workload heatmap for multiple users.
@@ -180,6 +181,7 @@ def get_workload_heatmap(
         week_start: Start of week (defaults to current week)
         department_id: Filter by department
         user_ids: Filter by specific user IDs
+        hide_empty: If True, exclude users with no tasks (default: True)
 
     Returns:
         List of UserWorkloadSummary objects
@@ -260,6 +262,10 @@ def get_workload_heatmap(
         )
         results.append(summary)
 
+    # Filter out users with no tasks if hide_empty is True
+    if hide_empty:
+        results = [r for r in results if r.task_count > 0]
+
     return results