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/api/workload/router.py

@@ -101,6 +101,10 @@ async def get_heatmap(
         None,
         description="Comma-separated list of user IDs to include"
     ),
+    hide_empty: bool = Query(
+        True,
+        description="Hide users with no tasks assigned for the week"
+    ),
     db: Session = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
@@ -133,8 +137,10 @@ async def get_heatmap(
 
     week_start, week_end = get_week_bounds(week_start)
 
-    # Try cache first
-    cached = get_cached_heatmap(week_start, department_id, accessible_user_ids)
+    # Try cache first (only use cache for default hide_empty=True)
+    cached = None
+    if hide_empty:
+        cached = get_cached_heatmap(week_start, department_id, accessible_user_ids)
     if cached:
         return WorkloadHeatmapResponse(
             week_start=week_start,
@@ -148,10 +154,12 @@ async def get_heatmap(
         week_start=week_start,
         department_id=department_id,
         user_ids=accessible_user_ids,
+        hide_empty=hide_empty,
     )
 
-    # Cache the result
-    set_cached_heatmap(week_start, summaries, department_id, accessible_user_ids)
+    # Cache the result (only cache when hide_empty=True, the default)
+    if hide_empty:
+        set_cached_heatmap(week_start, summaries, department_id, accessible_user_ids)
 
     return WorkloadHeatmapResponse(
         week_start=week_start,