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.

packages/client/schema-form/src/index.ts

@@ -11,6 +11,6 @@ export type {
   SchemaFieldContext, SchemaFormLabels, SchemaFormProps, SchemaFormSecret,
 } from './SchemaForm.tsx'
 export {
-  deletePath, getPath, hasPath, nodeKind, rehydrateSchema, setPath, unionChoices, validateDraft,
+  deletePath, getPath, hasPath, nodeAtPath, nodeKind, rehydrateSchema, setPath, unionChoices, validateDraft,
 } from './model.ts'
 export type { NodeKind, SchemaNode } from './model.ts'