Add bilingual French/English support with Hugo multilingual config

Configure Hugo multilingual mode (fr default, en secondary) with
Hextra's language-switch menu entry, and translate all existing
content pages to English using Hugo's per-file language suffix
convention (.en.md alongside .fr.md).

content/documentation/_index.en.md

@@ -0,0 +1,16 @@
+---
+title: Documentation
+cascade:
+  type: docs
+
+---
+<!-- markdownlint-disable MD033 MD034-->
+
+{{< hextra/hero-subtitle >}}
+  Comprehensive documentation and step-by-step practical guides
+{{< /hextra/hero-subtitle >}}
+
+{{< cards >}}
+  {{< card link="https://containerlab.dev/install/" title="ContainerLab" subtitle="How to Install ContainerLab" icon="endpoints" >}}
+  {{< card link="https://devpod.sh" title="DevPod" subtitle="A simple way to deploy Labs" icon="git" >}}  
+{{< /cards >}}