fix: drop PyYAML dep so verify job pytest passes

Store doc rules in bin/docs_rules.json (stdlib json). test_check_docs no
longer fails in the simulator job that only installs simulator/requirements.txt.

docs/improvement/ci-rules.md

@@ -2,7 +2,7 @@
 
 Automated checks for markdown in this repository. Enforced on every **pull request** and on **push to `main`** (including docs-only pushes that skip the simulator gate).
 
-Implementation: [`bin/check_docs.py`](../../bin/check_docs.py) reads [`bin/docs_rules.yaml`](../../bin/docs_rules.yaml).
+Implementation: [`bin/check_docs.py`](../../bin/check_docs.py) reads [`bin/docs_rules.json`](../../bin/docs_rules.json).
 
 Workflow: [`.github/workflows/release.yaml`](../../.github/workflows/release.yaml) job **`Verify documentation`**.
 
@@ -53,6 +53,6 @@ python bin/check_docs.py --warnings-as-errors   # treat section-link warnings as
 
 ## Changing rules
 
-1. Edit `bin/docs_rules.yaml` (paths, banned targets, preferred anchors).
+1. Edit `bin/docs_rules.json` (paths, banned targets, preferred anchors).
 2. Adjust `bin/check_docs.py` only when adding a new rule *type*.
 3. Add a row to the table above and mention it in the audit/improvement record if the change is significant.