Fix task type validation presentation and giant toast icons in admin panel

[lucas-matw-unq]

Description

When creating task types in the Admin panel (/admin/project/:id/data or /tasks), two issues occurred:

1. When entering duplicate task types or empty input, validation errors were either displayed as raw untranslated keys (admin.task_type_exists_error) or lacked user feedback.
2. The toast icons (check mark and exclamation mark) appeared gigantic across the screen because vue3-toastify/dist/index.css was not imported globally in main.js.

Proposed Fix

• Import vue3-toastify/dist/index.css globally in main.js.
• Add missing translation keys (task_type_exists_error, task_type_name_required) to es.json, en.json, and pt.json.
• Validate empty task type names in ProjectDetails.vue and present proper error messages.
• Add unit test suite to verify task type validation behavior.