l10n: add Swedish Cockpit translations

[yeager]

Summary

• add Swedish translations for the Borg Cockpit TUI
• choose Swedish from BORG_COCKPIT_LANGUAGE or the process locale
• keep the existing Borg-mode translator behavior unchanged
• cover Swedish, English fallback, and Borg-mode precedence

Validation

• isolated Python checks for the translator module
• git diff --check origin/master...HEAD

The repository test suite could not be started in this environment because the local Python installation lacks the unrelated platformdirs dependency; no generated files are included.

[yeager]

Closing this to follow the maintainer guidance in #10330: Cockpit localization is not planned while the feature is still evolving. The Swedish work will stay in the local translation archive and can be revisited if an official i18n path is introduced.