Tools: HF-24 wire snippets:check into the lint CI workflow

Runs `npm run snippets:check` (= extract + `git diff --exit-code` on
`test-utils/snippets/`) before the linter. Fails the lint job — same
gate as eslint — when a documented snippet has drifted from the
committed generated file. Closes the feedback loop the codegen
infrastructure was built for: docs become a load-bearing source of
truth, not a parallel artifact that drifts silently.

Companion to 6a441b3 (the codegen MVP); together these mean any
future edit to `docs/guide/currency-handling.md`'s adapter snippet must
either be regenerated locally or the CI will block the merge.

Author: marcin-kordas-hoc

.github/workflows/lint.yml

@@ -44,5 +44,8 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
+      - name: Check docs snippets are in sync with extracted source-of-truth
+        run: npm run snippets:check
+
       - name: Run linter
         run: npm run lint