Task/Issue URL:
https://app.asana.com/1/137249556945/project/1200204095367872/task/1216252715974135?focus=true
Tech Design URL (if applicable): 

### Description

- Translates everything in duckchat `donottranslate`

### Steps to test this PR

- [ ] Code review


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Resource-only i18n reshuffle with no logic changes; main risk is
translation/placeholder errors affecting UX or a11y strings in
non-English locales.
> 
> **Overview**
> This PR **localizes Duck.ai chat UI copy** that previously lived only
in English inside `donottranslate.xml`.
> 
> Those strings are **moved into** `values/strings-duckchat.xml`
(default English) and **mirrored in many `values-*/strings-duckchat.xml`
locales** (~64 entries each), covering native chat input,
model/reasoning pickers, attachments and limits, options menu,
accessibility labels, and related settings/Search Assist titles.
> 
> `donottranslate.xml` is **cleared** of that block so the same resource
names are now translatable. A handful of **existing strings are
tweaked** in individual locales (e.g. Danish new-tab toggle wording,
Greek informal *you*, French/Norwegian/Swedish “use without AI”
descriptions).
> 
> <sup>Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit
2e37295debf9139193cd6a05c9ca72b787af8b4d. Bugbot is set up for automated
code reviews on this repo. Configure
[here](https://www.cursor.com/dashboard/bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

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Co-authored-by: smartling <smartling@host-vm>