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>

frontend/package.json

@@ -9,10 +9,16 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "@fullcalendar/core": "^6.1.20",
+    "@fullcalendar/daygrid": "^6.1.20",
+    "@fullcalendar/interaction": "^6.1.20",
+    "@fullcalendar/react": "^6.1.20",
+    "@fullcalendar/timegrid": "^6.1.20",
+    "axios": "^1.6.0",
+    "frappe-gantt": "^1.0.4",
     "react": "^18.2.0",
     "react-dom": "^18.2.0",
-    "react-router-dom": "^6.21.0",
-    "axios": "^1.6.0"
+    "react-router-dom": "^6.21.0"
   },
   "devDependencies": {
     "@types/react": "^18.2.43",