fix(docs): use relearn notice shortcode instead of unsupported alert

[localai-bot]

What

The docs deploy (GitHub Pages) is failing on master at the Build site step:

Error: error building site: ... failed to extract shortcode:
template for shortcode "alert" not found
docs/content/features/image-generation.md:106:1

Failing run: https://github.com/mudler/LocalAI/actions/runs/27624864370/job/81683555291

Why

The Hugo theme in use is hugo-theme-relearn, which has no alert shortcode. Callouts everywhere else in the docs use the theme-supported notice shortcode (48 occurrences). A recently added vae_decode_only note in image-generation.md used {{% alert note %}}, which Hugo cannot resolve, breaking the build.

Fix

Convert the block from alert to notice:

-{{% alert note %}}
+{{% notice note %}}
 `vae_decode_only` is still accepted for backwards compatibility ...
-{{% /alert %}}
+{{% /notice %}}

This is the only remaining alert occurrence in docs/content.