docs: import AGENTS.md into CLAUDE.md (#794)

Use the @AGENTS.md import so Claude Code loads the contribution rules,
workflow and conventions automatically instead of relying on the agent to
follow the link. Keeps AGENTS.md as the single source of truth.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Fabian Hofmann <fab.hof@gmx.de>

Author: 3 people

CLAUDE.md

@@ -1,5 +1,8 @@
 # CLAUDE.md
 
 This project's guidance for AI agents — contribution rules, development workflow
-and project conventions — lives in [`AGENTS.md`](AGENTS.md). Read it before
-making changes, opening pull requests or issues, or writing comments.
+and project conventions — lives in [`AGENTS.md`](AGENTS.md), imported below so
+it loads automatically. Read it before making changes, opening pull requests or
+issues, or writing comments.
+
+@AGENTS.md