fix(i18n): complete Spanish translation for 'Hello World' section

[eloygnz]

No functional changes. Only documentation text updated in es.po.

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[eloygnz]

Hi @marioidival

First of all, thank you for your time reviewing this contribution. I completely understand that open source maintenance is demanding and reviews can take time.

About my workflow

I've been sending small, focused PRs (like this one) with the intention of:

• Making reviews faster and less noisy
• Reducing the risk of conflicts with other contributors
• Allowing incremental progress on the Spanish translation

However, I realize this approach might not align with the project's preferred workflow. If that's the case, I'm happy to adapt. Here are a few options I can follow:

1. Batch update: I can rebuild es.po locally and submit a single PR with all my translations up to date.
2. Larger PRs: I can continue with the base es.po but group changes into bigger, section-level PRs.
3. Your guidance: If you have a preferred format or process for i18n contributions, please let me know—I'll follow it.

No pressure at all; just want to make sure my contributions are as helpful and easy to merge as possible.

Notes on specific changes in this PR

For transparency, here's why these lines were adjusted:

Line	Change	Reason
989	Added missing article "el": "haciendo clic en el botón \"Reset\""	Spanish grammar requires the definite article here for natural phrasing.
994	Added trailing \n: "// Esta es la función main.\n"	Missing newline caused rendering issues in the generated HTML.
1011	Fixed typo: "text" → "texto"; improved preposition: "a la consola" → "en la consola"	"Texto" is the correct Spanish word; "en" is the standard preposition for output destinations in technical Spanish.
1033	Split "unsegundo" → "una segunda"; restructured: "una segunda macro \println!`"`	"Unsegundo" is a typo (should be "una segunda"); the restructured phrasing flows more naturally in Spanish technical documentation.

All changes are non-functional and only affect visible documentation text in es.po.

Verified locally

• MDBOOK_BOOK__LANGUAGE=es mdbook build passes without errors
• Rendered output checked at localhost:3000

Again, thank you for your work on this project. I'm happy to adjust this PR or future contributions in any way that better fits the project's needs. Just let me know what works best for you.