fix: rename language field to refugee language and enable multi-select

[Cy-fox]

Closes #388

Description

The "Language to translate" field in Accompanying Details only allowed selecting one language and the name did not match the intended purpose. It now shows as "Refugee language", allows selecting multiple languages via checkboxes, and sends the full array to the API.

Changes:

• Renamed field label from "Language to translate" to "Refugee language" in EN and DE translations
• Changed form field from single string to string array in schema and form state
• Switched EditableField from radio-list to checkbox-list to allow multi-select
• Submit handler now sends the full selected array instead of wrapping a single value

How to test:

1. Open an accompanying-type opportunity profile
2. Go to Accompanying Details and click Edit
3. Confirm the field is now labelled "Refugee language" and shows checkboxes
4. Select multiple languages, save, and confirm all selections are preserved

[nadavosa]

Correct upgrade — switching from single radio-list to multi-select checkbox-list, schema from z.string() to z.array(z.string()), and the display join logic all look right.

One heads-up: this PR touches the same AccompanyingDetails files as #346 (schema, helpers, edit, main component). Whichever merges second will need a rebase. Recommend merging this one first since #346 already has conflicts with develop.