i18n(fr): update route-data.mdx, frontmatter.mdx & sidebar.mdx

[ArmandPhilippot]

Description

Adds changes from #3644 to the French translations of reference/route-data.mdx, reference/frontmatter.mdx and guides/sidebar.mdx. Those are small changes, so I think a single PR should be fine.

I was confused by Lunaria... I don't know why for guides/sidebar, I see a PR authored
on Jul 16, 2025 in "source change history". 😅 But I checked, it seems everything is there!

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Latest commit: 7fed585

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Tracked Files

Locale	File	Note
fr	guides/sidebar.mdx	Localization changed, will be marked as complete.
fr	reference/frontmatter.md	Localization changed, will be marked as complete.
fr	reference/route-data.mdx	Localization changed, will be marked as complete.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[HiDeoo]

Looks perfect to me 🚀

Thanks for the updates 🙌