feat: add full Danish translation (#1146)

## Summary

* **What is the goal of this PR?** (e.g., Implements the new feature for
file uploading.)
A Danish translation for the GUI

* **What changes are included?**
Everything from
[`i18n.md`](https://github.com/crosspoint-reader/crosspoint-reader/blob/master/docs/i18n.md)

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## Additional Context

* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks,
  specific areas to focus on).

No

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### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**< YES | PARTIALLY | NO
>**_

Started translating myself, transitioned to having Claude Code do the
bulk of the translation. Read every translation myself and doubled
checked with a dictionary if I agreed with the translation made.

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Co-authored-by: Arthur Tazhitdinov <lisnake@gmail.com>

docs/i18n.md

@@ -13,6 +13,7 @@ This guide explains the multi-language support system in CrossPoint Reader.
 - Czech
 - Russian
 - Ukrainian
+- Danish
 
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