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>

frontend/public/locales/en/workload.json

@@ -30,13 +30,43 @@
     "overloaded": "Overloaded",
     "underutilized": "Underutilized"
   },
+  "table": {
+    "member": "Team Member",
+    "department": "Department",
+    "allocated": "Allocated",
+    "capacity": "Capacity",
+    "load": "Load",
+    "status": "Status"
+  },
   "status": {
     "balanced": "Balanced",
+    "normal": "Normal",
+    "warning": "Warning",
     "overloaded": "Overloaded",
+    "unavailable": "Unavailable",
     "underutilized": "Underutilized"
   },
   "empty": {
     "title": "No Workload Data",
-    "description": "Not enough data to display workload"
+    "description": "Not enough data to display workload",
+    "noTasks": "No one has been assigned tasks this week",
+    "hint": "Team members will appear here when they are assigned tasks with due dates in this week."
+  },
+  "options": {
+    "showAllUsers": "Show all users",
+    "showAllUsersHint": "(including users without tasks)"
+  },
+  "calculation": {
+    "title": "Workload Calculation",
+    "formula": "Workload = Weekly task estimated hours ÷ Personal weekly capacity × 100%",
+    "requirements": "Tasks must meet all conditions to be counted:",
+    "req1": "Task is assigned to the member",
+    "req2": "Task due date falls within the selected week",
+    "req3": "Task has estimated hours (original_estimate)",
+    "req4": "Task is not completed",
+    "thresholds": "Load Level Thresholds:",
+    "normal": "Normal: < 80%",
+    "warning": "Warning: 80% - 99%",
+    "overloaded": "Overloaded: ≥ 100%"
   }
 }