fix: use full s3 URLs for localized images

[brandonmcconnell]

Documentation changes

Ensures that theme images in localized documentation (es, fr, zh) are loaded from a full S3 URL instead of a relative path. This fixes an issue where images were not displaying correctly on localized versions of the documentation.

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Note

Low Risk
Documentation-only change that adjusts image URLs; main risk is broken images if the S3 path changes or becomes unavailable.

Overview
Switches localized themes.mdx pages (es, fr, zh) to load theme preview images via an absolute https://mintlify.s3... URL rather than /images/themes/..., ensuring images render correctly outside the default locale.

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