docs: Replace GitHub-style alerts with Docsy shortcodes

Problem

Some minikube site docs use GitHub-style alert syntax:

> [!WARNING]
> ...

> [!IMPORTANT]
> ...

This renders as plain blockquotes on minikube.sigs.k8s.io (Hugo/Docsy), not as styled warnings or notes.

Solution

Replace with Docsy shortcodes that render correctly:

Warning:

{{% alert title="Warning" color="warning" %}}
Your warning text here.
{{% /alert %}}

Important / note:

{{% alert title="Note" color="primary" %}}
Your note text here.
{{% /alert %}}

Info / tips (optional, for less urgent callouts):

{{% pageinfo color="info" %}}
Your info text here.
{{% /pageinfo %}}

Working examples in the repo:

• site/content/en/docs/contrib/releasing/binaries.md (warning)
• site/content/en/docs/handbook/host-access.md (note)
• site/content/en/docs/handbook/pushing.md (pageinfo)

Files to update

• site/content/en/docs/drivers/krunkit.md — [!IMPORTANT], [!WARNING]
• site/content/en/docs/drivers/vfkit.md — **IMPORTANT**: inline (convert to alert)
• site/content/en/docs/contrib/building/iso.md — [!IMPORTANT]

Search for other occurrences:

rg '\[!(WARNING|IMPORTANT|NOTE|TIP|CAUTION)' site/

Good first issue

• Small, docs-only change
• Clear before/after examples
• Verify rendering locally with make site (or the site docs build target)

Acceptance criteria

• No remaining GitHub-style > [!...] alerts under site/
• Converted callouts render as styled alerts on the published site