fix: use @AGENTS.md import syntax in CLAUDE.md

Repository-Defaults specifies CLAUDE.md must import AGENTS.md with the
'@AGENTS.md' syntax so Claude Code reads it natively, not as prose.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug

CLAUDE.md

@@ -1,3 +1 @@
-# Claude
-
-See [`AGENTS.md`](AGENTS.md) for all onboarding and guidance pointers for this repository.
+@AGENTS.md