Update and improve Croatian (hrvatski) (hr_HR) locale

[PeterDaveHello]

Description of Changes

In #2164, the previous use of Qwen2.5 7b (a smaller and less advanced AI model) was an earlier attempt that resulted in suboptimal quality and user experience. While relying solely on LLMs for translation is generally not ideal, adopting more advanced models like GPT-5 and Gemini 2.5 Pro allows us to address these earlier limitations and can ensure significantly better results, even for languages I do not understand.

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Checklist

General

• [ ] I have read the Contribution Guidelines
• [ ] I have read the Stirling-PDF Developer Guide (if applicable)
• [ ] I have read the How to add new languages to Stirling-PDF (if applicable)
• [ ] I have performed a self-review of my own code
• [ ] My changes generate no new warnings

Documentation

• [ ] I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• [ ] I have read the section Add New Translation Tags (for new translation tags only)

UI Changes (if applicable)

• [ ] Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• [ ] I have tested my changes locally. Refer to the Testing Guide for more details.

[stirlingbot[bot]]

🚀 Translation Verification Summary

🔄 Reference Branch: main-branch-messages_en_GB.properties

📃 File Check: messages_hr_HR.properties

1. Test Status: ✅ Passed
2. Test Status: ✅ Passed
3. Test Status: ✅ Passed

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✅ Overall Check Status: Success

Thanks @PeterDaveHello for your help in keeping the translations up to date.

[PeterDaveHello]

@Frooodle do you have a minute to take a quick look?

[PeterDaveHello]

@Frooodle are we good to merge here?