feat: implement custom fields, gantt view, calendar view, and file encryption

- Custom Fields (FEAT-001):
  - CustomField and TaskCustomValue models with formula support
  - CRUD API for custom field management
  - Formula engine for calculated fields
  - Frontend: CustomFieldEditor, CustomFieldInput, ProjectSettings page
  - Task list API now includes custom_values
  - KanbanBoard displays custom field values

- Gantt View (FEAT-003):
  - TaskDependency model with FS/SS/FF/SF dependency types
  - Dependency CRUD API with cycle detection
  - start_date field added to tasks
  - GanttChart component with Frappe Gantt integration
  - Dependency type selector in UI

- Calendar View (FEAT-004):
  - CalendarView component with FullCalendar integration
  - Date range filtering API for tasks
  - Drag-and-drop date updates
  - View mode switching in Tasks page

- File Encryption (FEAT-010):
  - AES-256-GCM encryption service
  - EncryptionKey model with key rotation support
  - Admin API for key management
  - Encrypted upload/download for confidential projects

- Migrations: 011 (custom fields), 012 (encryption keys), 013 (task dependencies)
- Updated issues.md with completion status

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

openspec/changes/archive/2026-01-05-add-custom-fields/tasks.md

@@ -0,0 +1,82 @@
+# Tasks: Add Custom Fields
+
+## Backend Tasks
+
+### 1. Create CustomField and TaskCustomValue models
+- [x] Create `backend/app/models/custom_field.py` with CustomField model
+- [x] Create `backend/app/models/task_custom_value.py` with TaskCustomValue model
+- [x] Update `backend/app/models/__init__.py` to export new models
+- [x] Create Alembic migration for new tables
+- **驗證**: Migration 成功執行，tables 建立正確
+
+### 2. Create Custom Fields API endpoints
+- [x] Create `backend/app/api/custom_fields/router.py`
+- [x] Implement `POST /api/projects/{project_id}/custom-fields` - 新增欄位
+- [x] Implement `GET /api/projects/{project_id}/custom-fields` - 列出欄位
+- [x] Implement `PUT /api/custom-fields/{field_id}` - 更新欄位
+- [x] Implement `DELETE /api/custom-fields/{field_id}` - 刪除欄位
+- [x] Add permission checks (only project owner/manager can manage fields)
+- [x] Register router in main.py
+- **驗證**: API endpoints 可正常呼叫，權限檢查正確
+
+### 3. Implement formula calculation engine
+- [x] Create `backend/app/services/formula_service.py`
+- [x] Implement formula parsing (extract field references)
+- [x] Implement formula validation (detect circular references)
+- [x] Implement formula calculation
+- [x] Add unit tests for formula service
+- **驗證**: 公式計算正確，循環引用被拒絕
+
+### 4. Integrate custom values with Tasks API
+- [x] Modify `TaskCreate` schema to accept `custom_values`
+- [x] Modify `TaskUpdate` schema to accept `custom_values`
+- [x] Modify `TaskResponse` schema to include `custom_values`
+- [x] Update `create_task` endpoint to save custom values
+- [x] Update `update_task` endpoint to save custom values
+- [x] Update `get_task` endpoint to return custom values
+- [x] Trigger formula recalculation on value change
+- **驗證**: 任務 CRUD 包含自定義欄位值
+
+### 5. Add backend tests
+- [x] Test custom field CRUD operations
+- [x] Test permission checks
+- [x] Test formula calculation
+- [x] Test task integration with custom values
+- **驗證**: 所有測試通過 (20/20 tests passed)
+
+## Frontend Tasks
+
+### 6. Create Custom Fields management UI
+- [x] Create `frontend/src/pages/ProjectSettings.tsx` or extend existing
+- [x] Create `frontend/src/components/CustomFieldEditor.tsx` - 欄位編輯表單
+- [x] Create `frontend/src/components/CustomFieldList.tsx` - 欄位列表
+- [x] Add custom fields API service in `frontend/src/services/customFields.ts`
+- **驗證**: 可在專案設定中管理自定義欄位
+
+### 7. Dynamic field rendering in Task forms
+- [x] Create `frontend/src/components/CustomFieldInput.tsx` - 動態欄位輸入
+- [x] Integrate into TaskDetailModal.tsx
+- [x] Integrate into task creation form
+- [x] Handle different field types (text, number, dropdown, date, person)
+- [x] Display formula fields as read-only
+- **驗證**: 任務表單正確顯示和儲存自定義欄位
+
+### 8. Display custom fields in task views
+- [x] Add custom field columns to List view
+- [x] Display custom field values in Kanban cards (optional, configurable)
+- [x] Add column visibility toggle for custom fields
+- **驗證**: 自定義欄位值在各視角中正確顯示
+
+## Task Dependencies
+
+```
+[1] Models -> [2] API -> [4] Task Integration -> [5] Tests
+                    \
+                      [3] Formula Engine /
+
+[6] Management UI -> [7] Task Forms -> [8] View Display
+```
+
+- Tasks 1-5 (Backend) 可平行於 Tasks 6-8 (Frontend) 開發
+- Task 2 完成後 Task 6 可開始（需要 API）
+- Task 4 完成後 Task 7 可開始（需要 Task API 支援 custom values）