Add Portuguese localized page and redirect support

[Telucero]

Description

• Added a Portuguese 404 content page that uses the shared 404 template, hides the left navigation and table of contents, and is excluded from search.
• Added a minimal 404 redirect script that reads supported locales from the page (no hard-coded languages), detects locale prefixes in the URL, redirects to the locale-specific 404 page, supports subpath hosting, and avoids redirect loops.
• Automated babbel files

Related to mkdocs PR-101

Checklist

• I have added a label to this PR 🏷️
• I have run my changes through Grammarly
• If this page requires a disclaimer, I have added one
• If pages have been moved around, I have created an additional PR in tanssi-mkdocs to update redirects

[Copilot]

Pull request overview

Adds localized (Portuguese) 404 handling and supporting infrastructure for the docs site, including navigation and i18n catalog updates.

Changes:

• Added a Portuguese 404.md page using the shared 404.html template and excluded it from search.
• Updated pt/.nav.yml to include the 404 page and adjust Portuguese navigation structure/labels.
• Added a locale-aware 404 redirect script and regenerated Babel .po files for en and pt.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
pt/404.md	Adds a PT 404 page using the shared 404 template with nav/toc hidden and search excluded.
pt/.nav.yml	Updates Portuguese navigation structure and adds the 404 page to nav.
javascript/404-redirect.js	Adds a minimal client-side redirect script for locale-prefixed 404 routing.
i18n/pt/LC_MESSAGES/messages.po	Regenerated Portuguese gettext catalog/header and message ordering.
i18n/en/LC_MESSAGES/messages.po	Regenerated English gettext catalog/header and message ordering.

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