feat: add Dutch locale label

[huulie]

Summary

Adds Dutch (nl) to the UVdesk core-framework locale label map so the Detox@Home deployment can render the sidebar language selector when nl is enabled in app_locales.

Context

This complements the Dutch translation rollout in the Detox@Home community-skeleton fork:

• feat: add Dutch translations uvdesk_community-skeleton#4 added generic Dutch translations.
• feat: adapt Dutch translations for Detox@Home uvdesk_community-skeleton#3 adapted the Dutch wording for Detox@Home.
• chore: use Detox@Home core framework fork uvdesk_community-skeleton#5 wires the Detox@Home community-skeleton deployment branch to this core-framework fork branch.

Without this core-framework locale entry, /nl/... routes can load translations but the support dashboard fails while rendering uvdesk_service.getLocales().

Validation

• Ran git diff --check.
• Could not run php -l locally because php is not installed in this environment.