fix(examples): bind the multi-tenant demos to loopback (#72)

cmcp-runtime now refuses to start tokenless on a non-loopback address:

  CONFIG_ERROR: Tokenless development mode may only bind to a loopback
  address. Use 127.0.0.1:<port>, localhost:<port>, or [::1]:<port>, or
  configure CMCP_BEARER_TOKEN for non-loopback access.

Both multi-tenant configs bind 0.0.0.0:8443 and the smoke workflow runs them
under CMCP_DEV_MODE=1, so the gateway aborted at startup and "Wait for gateway"
timed out. Nothing had run on this repo since 2026-08-03, so it went unnoticed
for a week.

Loopback rather than a bearer token because these are demo configs run locally
and by smoke: the smoke job already talks to localhost:8443, and an example that
ships 0.0.0.0 with no token is not a topology anyone should copy.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: imran-siddique

multi-tenant-saas/cmcp-config-metzler-eu.yaml

@@ -1,6 +1,6 @@
 policy_bundle_path: ./tenants/metzler-eu/policy
 catalog_path: ./catalog.json
-listen_addr: 0.0.0.0:8443
+listen_addr: 127.0.0.1:8443
 audit_db_path: ./audit-metzler-eu.db
 attestation:
   provider: auto

multi-tenant-saas/cmcp-config-summit-us.yaml

@@ -1,6 +1,6 @@
 policy_bundle_path: ./tenants/summit-us/policy
 catalog_path: ./catalog.json
-listen_addr: 0.0.0.0:8443
+listen_addr: 127.0.0.1:8443
 audit_db_path: ./audit-summit-us.db
 attestation:
   provider: auto