docs: write Give a Teammate Deploy Access to One Stack tutorial (#1800)

Adds a new Tutorials entry (not part of the original 14-page batch)
covering scoped RBAC permissions: create a Viewer account, grant a
Deployer scope on one stack, and verify the boundary from both the
teammate's session and the audit log.

docs/docs.json

@@ -236,6 +236,7 @@
             "group": "Secure & integrate",
             "pages": [
               "tutorials/set-up-sso",
+              "tutorials/grant-scoped-stack-access",
               "tutorials/configure-environment-guardrails",
               "tutorials/set-up-a-webhook",
               "tutorials/resolve-stack-drift"