feat(policy): netkingdom maturity-gated publication-scope policy

Token scope is now bound to package maturity, gated on netkingdom's own maturity:
- maturity-build -> gitea-wide, maturity-test -> org-wide, maturity-prod -> repo-scoped
  (scope narrows as stakes rise; broad tokens only for low-stakes build artifacts)
- the graduated table is DORMANT until netkingdom reaches production grade; until
  then every lane clamps to repo-scope, injected as NPM_AUTH_TOKEN (fail-safe)
- token env-var name signals blast radius: NPM_AUTH_TOKEN (repo default),
  NPM_AUTH_COULOMB_TOKEN (org), NPM_AUTH_GITEA_TOKEN (gitea), NPM_AUTH_WHYNOT_TOKEN
  (npm scope, defined but unused), NPM_AUTH_WHYNOTDESIGN (explicit repo)

netkingdom is at maturity-build today, so whynot-design resolves to repo-scope /
NPM_AUTH_TOKEN. Flip netkingdom_maturity to maturity-prod to activate graduation.

- policies/netkingdom-publication-scope.yaml: the policy data + gate
- publication_policy.py: load + resolve (clamp/active, env naming, override)
- exec delivery injects under the resolved env-var name (was fixed SE_NPM_TOKEN)
- catalog lane carries delivery_config.npm.maturity
- new CLI: `secrets-engine policy publication <lane>`
- docs/publication-scope-policy.md; tests for clamp, graduation, naming, override

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_exec_delivery.py

@@ -12,11 +12,11 @@ def test_registry_authkey_strips_scheme_and_trails_slash():
 
 def test_npm_userconfig_writes_registry_and_token_ref_not_value():
     registry = "https://gitea.coulomb.social/api/packages/coulomb/npm/"
-    with _npm_userconfig(registry, "@whynot") as path:
+    with _npm_userconfig(registry, "@whynot", "NPM_AUTH_TOKEN") as path:
         body = path.read_text()
         assert f"@whynot:registry={registry}" in body
         # token is referenced via env expansion, never written literally
-        assert "${SE_NPM_TOKEN}" in body
+        assert "${NPM_AUTH_TOKEN}" in body
         assert "//gitea.coulomb.social/api/packages/coulomb/npm/:_authToken" in body
         # file is mode 0600
         assert (path.stat().st_mode & 0o077) == 0