feat(apiproxy): settings/credentials/llm wire domains, frames, and write guard

Eight compiler-locked methods: settings.describe/update/replace serve
redacted layered namespace views (secrets structurally absent from every
layer, write-only in the update direction) and fold seam refusals into
settings-rejected; credentials.describe/set/unset expose value-free views
with credential-rejected on shadowed writes; llm.providers merges the
configurable directory with live routes and llm.models claims the
host-scoped catalog reservation through the buildModelCatalog extraction
session.models now shares. Three HostFrame invalidations bridge the seam
events (host/settings-changed, host/credentials-changed,
host/models-changed), and the connection route generalizes the native-
dialog check into a privileged-method set covering all four writes. The
fixture and both fake clients grow the same face.

pnpm-lock.yaml

@@ -2861,6 +2861,9 @@ importers:
       '@deepseek-ai/dsh-commands':
         specifier: workspace:^
         version: link:../../ui/commands
+      '@deepseek-ai/dsh-credentials':
+        specifier: workspace:^
+        version: link:../../credentials/credentials
       '@deepseek-ai/dsh-goal':
         specifier: workspace:^
         version: link:../../goal/goal
@@ -2879,6 +2882,9 @@ importers:
       '@deepseek-ai/dsh-session-projection-cache':
         specifier: workspace:^
         version: link:../../session-projection/session-projection-cache
+      '@deepseek-ai/dsh-settings':
+        specifier: workspace:^
+        version: link:../../settings/settings
       '@deepseek-ai/dsh-skill':
         specifier: workspace:^
         version: link:../../skill/skill