i18n: Translate new keys for pt-BR

[JohnnyMendesC]

References

• No specific issue ticket. Addresses pending translation keys in the codebase.

Description

This PR updates the Portuguese (Brazil) translation file (src/assets/i18n/pt-BR.json5). It addresses approximately 290 keys previously marked as // TODO New key - Add a translation and // TODO Source message changed - Revise the translation, covering generic messages, admin curation tasks, bitstream formats, external login, and LDN/COAR Notify services.

Instructions for Reviewers

List of changes in this PR:

• Translated ~290 keys marked as TODO.
• Removed the // TODO New key - Add a translation and // TODO Source message changed - Revise the translation.

Guidance for testing:

1. Switch the UI language to Português (Brasil).
2. Verify that the newly translated keys (e.g., in Admin > Curation Tasks or LDN Services) appear correctly and are not falling back to English.

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