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/common.json

@@ -92,7 +92,15 @@
     "title": "Notifications",
     "markAllRead": "Mark all as read",
     "noNotifications": "No notifications",
-    "viewAll": "View all"
+    "empty": "No notifications",
+    "viewAll": "View all",
+    "refresh": "Refresh",
+    "time": {
+      "justNow": "Just now",
+      "minutesAgo": "{{count}}m ago",
+      "hoursAgo": "{{count}}h ago",
+      "daysAgo": "{{count}}d ago"
+    }
   },
   "pagination": {
     "page": "Page {{page}}",