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>

openspec/changes/archive/2026-01-09-add-delete-capability/proposal.md

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+# Proposal: Add Delete Capability for Spaces and Projects
+
+## Summary
+Enable users to delete workspaces (spaces) and projects from the frontend UI. The backend already supports soft deletion, but the frontend lacks the necessary UI components and service functions.
+
+## Problem Statement
+Currently, users cannot delete spaces or projects from the UI even though:
+1. Backend DELETE endpoints exist (`DELETE /spaces/{id}`, `DELETE /projects/{id}`)
+2. Both implement soft-delete (setting `is_active = False`)
+3. Project deletion includes audit logging
+
+Users must access the database directly or use API tools to delete items, which is not user-friendly.
+
+## Proposed Solution
+Add frontend UI components and service functions to enable deletion:
+
+1. **Frontend Services**: Add `deleteSpace()` and `deleteProject()` functions
+2. **Spaces Page**: Add delete button with confirmation dialog
+3. **Projects Page**: Add delete button with confirmation dialog
+4. **Translations**: Add i18n strings for delete UI elements
+
+## Scope
+
+### In Scope
+- Delete button UI for spaces (owner only)
+- Delete button UI for projects (owner only)
+- Confirmation dialogs with clear warning messages
+- i18n translations (zh-TW, en)
+- Audit trail (already implemented in backend for projects)
+
+### Out of Scope
+- Hard delete (permanent removal from database)
+- Restore/undelete functionality
+- Cascading delete behavior changes (current soft-delete preserves child items)
+- Bulk delete operations
+
+## Impact Analysis
+
+### Affected Components
+| Component | Change Type | Description |
+|-----------|-------------|-------------|
+| `frontend/src/services/spaces.ts` | NEW | Add deleteSpace function |
+| `frontend/src/services/projects.ts` | MODIFY | Add deleteProject function |
+| `frontend/src/pages/Spaces.tsx` | MODIFY | Add delete button and dialog |
+| `frontend/src/pages/Projects.tsx` | MODIFY | Add delete button and dialog |
+| `frontend/public/locales/*/spaces.json` | MODIFY | Add delete translations |
+| `frontend/public/locales/*/projects.json` | MODIFY | Add delete translations |
+
+### Dependencies
+- Backend DELETE endpoints (already implemented)
+- Audit service (already integrated for project deletion)
+- ToastContext for success/error notifications (already available)
+
+## Risks & Mitigations
+
+| Risk | Likelihood | Impact | Mitigation |
+|------|------------|--------|------------|
+| Accidental deletion | Medium | High | Require typed confirmation for spaces with projects |
+| Permission confusion | Low | Medium | Clear "owner only" messaging |
+
+## Success Criteria
+1. Space owner can delete empty spaces with confirmation
+2. Space owner can delete spaces with projects (with strong warning)
+3. Project owner can delete projects with confirmation
+4. All deletions are logged in audit trail
+5. UI shows appropriate error messages for non-owners