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>

backend/app/main.py

@@ -34,6 +34,9 @@ from app.api.attachments import router as attachments_router
 from app.api.triggers import router as triggers_router
 from app.api.reports import router as reports_router
 from app.api.health import router as health_router
+from app.api.custom_fields import router as custom_fields_router
+from app.api.task_dependencies import router as task_dependencies_router
+from app.api.admin import encryption_keys as admin_encryption_keys_router
 from app.core.config import settings
 
 app = FastAPI(
@@ -76,6 +79,9 @@ app.include_router(attachments_router)
 app.include_router(triggers_router)
 app.include_router(reports_router)
 app.include_router(health_router)
+app.include_router(custom_fields_router)
+app.include_router(task_dependencies_router)
+app.include_router(admin_encryption_keys_router.router)
 
 
 @app.get("/health")