feat: Implement interactive Vikunja task management

This commit introduces a `ConversationHandler` for the `/vik` command, replacing the previous simple command.

The new implementation provides an interactive menu for users with admin permissions to:
- View their tasks from a hardcoded project (ID 1).
- Add new tasks to the same project.

The changes include:
- A new `ConversationHandler` in `app/modules/vikunja.py` to manage the interactive flow.
- Integration of the new handler in `app/main.py`.
- Removal of the old `/vik` command handler.
- A fix in `test_vikunja.py` to correctly load environment variables.

test_vikunja.py

@@ -5,8 +5,7 @@ from dotenv import load_dotenv
 from pathlib import Path
 
 # Cargar variables de entorno
-env_path = Path(__file__).parent.parent / '.env'
-load_dotenv(dotenv_path=env_path)
+load_dotenv()
 
 VIKUNJA_API_URL = os.getenv("VIKUNJA_API_URL", "https://tasks.soul23.cloud/api/v1")
 VIKUNJA_API_TOKEN = os.getenv("VIKUNJA_API_TOKEN")