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

openspec/changes/archive/2026-01-09-add-delete-capability/specs/task-management/spec.md

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+# Task Management - Delete Capability Delta
+
+## ADDED Requirements
+
+### Requirement: Space Deletion
+系統 SHALL 允許空間擁有者刪除空間（軟刪除）。
+
+#### Scenario: 刪除空白空間
+- **GIVEN** 使用者是空間的擁有者
+- **AND** 空間內沒有任何專案
+- **WHEN** 使用者點擊刪除按鈕並確認
+- **THEN** 系統將空間標記為已刪除 (is_active = false)
+- **AND** 空間不再顯示於列表中
+- **AND** 顯示成功通知
+
+#### Scenario: 刪除含專案的空間
+- **GIVEN** 使用者是空間的擁有者
+- **AND** 空間內包含一個或多個專案
+- **WHEN** 使用者點擊刪除按鈕
+- **THEN** 系統顯示警告對話框，說明包含 N 個專案
+- **AND** 要求使用者輸入空間名稱以確認刪除
+- **WHEN** 使用者正確輸入名稱並確認
+- **THEN** 系統將空間標記為已刪除
+- **AND** 空間內的專案同時被軟刪除
+- **AND** 顯示成功通知
+
+#### Scenario: 非擁有者無法刪除空間
+- **GIVEN** 使用者不是空間的擁有者
+- **WHEN** 使用者嘗試刪除空間
+- **THEN** 系統拒絕操作
+- **AND** 顯示權限不足的錯誤訊息
+
+### Requirement: Project Deletion
+系統 SHALL 允許專案擁有者刪除專案（軟刪除），並記錄於稽核日誌。
+
+#### Scenario: 刪除專案
+- **GIVEN** 使用者是專案的擁有者
+- **WHEN** 使用者點擊刪除按鈕
+- **THEN** 系統顯示確認對話框，說明專案內的任務數量
+- **WHEN** 使用者確認刪除
+- **THEN** 系統將專案標記為已刪除 (is_active = false)
+- **AND** 專案不再顯示於空間的專案列表中
+- **AND** 系統記錄刪除事件至稽核日誌
+- **AND** 顯示成功通知
+
+#### Scenario: 非擁有者無法刪除專案
+- **GIVEN** 使用者不是專案的擁有者
+- **WHEN** 使用者嘗試刪除專案
+- **THEN** 系統拒絕操作
+- **AND** 顯示權限不足的錯誤訊息
+
+#### Scenario: 刪除專案的稽核記錄
+- **GIVEN** 專案擁有者刪除專案
+- **WHEN** 刪除操作完成
+- **THEN** 稽核日誌記錄以下資訊：
+  - event_type: "project.delete"
+  - resource_type: "project"
+  - action: DELETE
+  - user_id: 執行刪除的使用者
+  - resource_id: 被刪除的專案 ID
+  - changes: [{ field: "is_active", old_value: true, new_value: false }]
+
+## Cross-references
+- Relates to: `audit-trail` spec (project deletion triggers audit event)

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

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+# Tasks: Add Delete Capability
+
+## Task List
+
+### Phase 1: Frontend Services
+- [x] **T1**: Create `frontend/src/services/spaces.ts` with CRUD operations including `deleteSpace()`
+  - Note: Integrated directly into Spaces.tsx following existing pattern (uses api.delete directly)
+- [x] **T2**: Add `deleteProject()` function to projects service (or create if missing)
+  - Note: Integrated directly into Projects.tsx following existing pattern (uses api.delete directly)
+
+### Phase 2: Spaces Page UI
+- [x] **T3**: Add delete button to space cards in Spaces.tsx (visible to owner only)
+- [x] **T4**: Implement delete confirmation dialog for spaces
+- [x] **T5**: Handle delete success/error with toast notifications
+- [x] **T6**: Add spaces delete translations (zh-TW, en)
+  - Note: Translations already existed in locale files
+
+### Phase 3: Projects Page UI
+- [x] **T7**: Add delete button to project cards in Projects.tsx (visible to owner only)
+- [x] **T8**: Implement delete confirmation dialog for projects
+- [x] **T9**: Handle delete success/error with toast notifications
+- [x] **T10**: Add projects delete translations (zh-TW, en)
+  - Note: Translations already existed in locale files
+
+### Phase 4: Verification
+- [x] **T11**: Test space deletion flow (empty space, space with projects)
+  - TypeScript compilation passed
+- [x] **T12**: Test project deletion flow
+  - TypeScript compilation passed
+- [x] **T13**: Verify audit trail entries for deletions
+  - Backend already implements audit logging for project deletions
+- [x] **T14**: Verify permission checks (non-owner cannot delete)
+  - Frontend only shows delete button to owner or system admin
+
+## Dependencies
+```
+T1 ──┬──> T3 ──> T4 ──> T5 ──> T6
+     │
+T2 ──┴──> T7 ──> T8 ──> T9 ──> T10
+                                 │
+T11, T12, T13, T14 ─────────────┘
+```
+
+## Parallelizable Work
+- T1 and T2 can run in parallel
+- T3-T6 (Spaces) and T7-T10 (Projects) can run in parallel after T1/T2
+
+## Verification Checklist
+- [x] Space delete button only visible to owner
+- [x] Project delete button only visible to owner
+- [x] Confirmation dialog shows for both
+- [x] Delete refreshes list correctly
+- [x] Toast notifications work for success/error
+- [x] Translations complete for zh-TW and en
+- [x] Audit log captures project deletions