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/models/project.py

@@ -28,6 +28,7 @@ class Project(Base):
         nullable=False
     )
     status = Column(String(50), default="active", nullable=False)
+    is_active = Column(Boolean, default=True, nullable=False)
     department_id = Column(String(36), ForeignKey("pjctrl_departments.id"), nullable=True)
     created_at = Column(DateTime, server_default=func.now(), nullable=False)
     updated_at = Column(DateTime, server_default=func.now(), onupdate=func.now(), nullable=False)