feat(ui-models): schema-driven provider configuration page

The Models settings section joins llm.providers (the configurable
directory with live state), settings.describe (schemas, layered redacted
values, secret slots), and credentials.describe (value-free badges) into
provider rows with one editor card at a time. The editor renders the
provider's profile subtree through dsh-client-schema-form; the
credential-ref role mounts a control that shows configured/source state
and stores keys write-only through credentials.set. Apply without
removals merges a minimal patch (stored secrets outside it survive);
apply after a reset — and row deletion — replace the user section so
removals land. The client runtime bridges the three new host frames to
typed ctx events (settings/credentials/models changed), the page
refetches on any of them once loaded, and ui-model's per-session picker
directories reload on models/changed so a settings-born route appears in
open pickers without a reopen.

tsconfig.base.json

@@ -118,6 +118,8 @@
       "@deepseek-ai/dsh-host-webserver": ["./packages/host/webserver/src"],
       "@deepseek-ai/dsh-client-ui-slots": ["./packages/client/ui-slots/src"],
       "@deepseek-ai/dsh-client-ui-primitives": ["./packages/client/ui-primitives/src"],
+      "@deepseek-ai/dsh-client-schema-form": ["./packages/client/schema-form/src"],
+      "@deepseek-ai/dsh-client-schema-form/invariant": ["./packages/client/schema-form/src/invariant.ts"],
       "@deepseek-ai/dsh-client-web-react": ["./packages/client/web-react/src"],
       "@deepseek-ai/dsh-client-connection": ["./packages/client/connection/src"],
       "@deepseek-ai/dsh-client-hmr": ["./packages/client/hmr/src"],