docs: define a seam as the (Service, Service provider, Consumer) trio

docs/subsystems/credentials.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write docs/subsystems/credentials.md
-credentials.md: 0bc2224ac039addc795d3806e8c85004f2bb84a7
-credentials.zh.md: f236b0b2daef85784308f10dbcfc67db84c42234
+credentials.md: 84b156e366b2f4d0aeaba11b1b8d005ff59ad11d
+credentials.zh.md: c12191529e4324aed57b0ec8870fdca5c4dcae8a