chore(agents): load AGENTS.md in Claude Code and guard its rules

Claude Code discovers CLAUDE.md but not AGENTS.md, so the contributor
instructions were loading for nobody. The import shim is what our own docs
already recommend to users in docs/edge/en/guides/coding-tools/agents-md.mdx.

The PreToolUse guard enforces only rules already written in CONTRIBUTING.md
and AGENTS.md, so it adds no policy of its own.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ASfWmW3RGy4qAQm6s8U9jH

.pre-commit-config.yaml

@@ -61,6 +61,18 @@ repos:
         language: system
         pass_filenames: false
         stages: [pre-push, manual]
+  - repo: local
+    hooks:
+      - id: agent-guard-hook
+        name: agent-guard-hook
+        # --confcutdir keeps the root conftest out: it assumes every test lives
+        # under lib/<package>/tests/, which these do not.
+        entry: >-
+          bash -c 'source .venv/bin/activate && uv run pytest
+          .claude/hooks/test_guard.py -q --confcutdir=.claude/hooks'
+        language: system
+        pass_filenames: false
+        files: ^\.claude/hooks/
   - repo: https://github.com/commitizen-tools/commitizen
     rev: v4.10.1
     hooks: