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/tasks/router.py

@@ -406,6 +406,28 @@ async def update_task(
     update_data = task_data.model_dump(exclude_unset=True)
     custom_values_data = update_data.pop("custom_values", None)
 
+    # Track old assignee for workload cache invalidation
+    old_assignee_id = task.assignee_id
+
+    # Validate assignee_id if provided
+    if "assignee_id" in update_data and update_data["assignee_id"]:
+        assignee = db.query(User).filter(User.id == update_data["assignee_id"]).first()
+        if not assignee:
+            raise HTTPException(
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail="Assignee not found",
+            )
+
+    # Validate status_id if provided
+    if "status_id" in update_data and update_data["status_id"]:
+        from app.models.task_status import TaskStatus
+        task_status = db.query(TaskStatus).filter(TaskStatus.id == update_data["status_id"]).first()
+        if not task_status:
+            raise HTTPException(
+                status_code=status.HTTP_404_NOT_FOUND,
+                detail="Status not found",
+            )
+
     # Get the proposed start_date and due_date for validation
     new_start_date = update_data.get("start_date", task.start_date)
     new_due_date = update_data.get("due_date", task.due_date)
@@ -486,6 +508,15 @@ async def update_task(
     if "original_estimate" in update_data and task.assignee_id:
         invalidate_user_workload_cache(task.assignee_id)
 
+    # Invalidate workload cache if assignee changed
+    if "assignee_id" in update_data:
+        # Invalidate old assignee's cache
+        if old_assignee_id and old_assignee_id != task.assignee_id:
+            invalidate_user_workload_cache(old_assignee_id)
+        # Invalidate new assignee's cache
+        if task.assignee_id:
+            invalidate_user_workload_cache(task.assignee_id)
+
     # Publish real-time event
     try:
         await publish_task_event(