v1.16.0: OpenBao as central secrets store + vault broker + UI rework

- Boot: bao-conf.init('sso-manager') replaces conf_manager; deep-merges
  secret/sso-manager/conf over file config (fail-soft). Scoped VAULT_TOKEN
  (policy sso-broker), never root.
- /api/vault reworked: middleware.auth -> scopeGuard -> token-injecting
  proxy. vault_broker.js mints Redis-cached per-user (user-<uid>) /
  per-admin (sso-admin) tokens via the sso-broker role; scopeGuard enforces
  path prefix on top of the OpenBao policy. Client auth-token stripped.
- vault UI renamed (vaultwarden.ejs -> vault.ejs), /vault route auth-gated,
  role-scoped: users see only secret/users/<uid>/, admins get free-form +
  Apps mint tab (secret/apps/<name>/*, token shown once).
- api_conf.js writes via bao-conf.set('sso-manager', ...).
- Remediation: config/*-secrets.js untracked+gitignored, test_plugins.js
  deleted, proxy-secrets.js.example placeholder added. Secrets remain in
  git history; provider-side rotation is the real fix.

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

.gitignore

@@ -86,6 +86,11 @@ ops/cookbooks/vendor
 secrets.json
 secrets.js
 
+# Per-deployment secret files (real LDAP/SMTP/jwtSecret + generated OAuth
+# creds). theta-env bind-mounts ./config and generates/fills these at setup;
+# they must never be committed. The empty *.example templates ARE tracked.
+config/*-secrets.js
+
 # Jekyll build artifact (GitHub Pages builds remotely; ignore locally)
 docs/_site