commands/az-hilfe.md: slash-command counterpart to the az-hilfe skill —
description frontmatter, template body using $ARGUMENTS and $1 topic
placeholder, kebab-case name → /az-hilfe after fleet delivery.
Four invalid command fixtures under tests/fixtures/commands/invalid/
covering all README-documented failure modes: missing frontmatter,
missing description, empty description value, umlaut filename.
Closes az-agent-defaults-gj1
