feat(mise): Add toolbox name header in generated conf.d files

Addresses PR feedback: each conf.d/<toolbox>.toml now starts with a
"# Toolbox: <name>" comment, matching the previous inline config.toml
layout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GA4dAzARMnLz1G9AmQkYYn

.chezmoitemplates/mise-toolbox-conf

@@ -2,6 +2,8 @@
 {{/* Expects data: (merge (dict "toolboxName" "<name>") .) */}}
 {{- $toolboxName := .toolboxName -}}
 {{ includeTemplate "chezmoi-managed-header" . }}
+# Toolbox: {{ $toolboxName }}
+
 [tools]
 {{- $toolsList := index .tools.toolboxes $toolboxName }}
 {{- range $tool := $toolsList }}