[TCE] Draft Danish (da) YAML

[veganstraightedge]

About this draft

Auto-generated starter for a new language's TCE YAML. Imperfect and incomplete — a decent starting point but needs manual intervention to finish.

This file is da.yml — a YAML draft. It is imperfect: expect misaligned section boundaries, missing short UI labels, and English-language image_alt placeholders carried over from en.yml.

Scope of this PR

This PR only adds the draft file. It does not wire up the language. A full TCE language migration also needs:

• Entries in config/application.rb (path_ltr_locales or path_rtl_locales)
• Entry in ToChangeEverythingController::LTR_TO_CHANGE_ANYTHING_YAMLS (or RTL)
• New .scss stylesheet in app/assets/stylesheets/to_change_everything/
• @import line in app/assets/stylesheets/to_change_everything.scss
• HTML formatting (<p>, <br>, <span class="bold">) around body text
• Translated layouts.to_change_everything section (menu/toc labels)
• Short UI labels (video_cte, pdf_cte_html, take_flight_html, next_text) that the extractor couldn't pick up
• Correct image_alt descriptions (currently copied from English)

For the complete process, see docs/to-change-everything-guide.md. Reference PRs: #5200 (Deutsch), #5201 (Polski).