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/ui-model/src/client/service.ts

@@ -44,6 +44,14 @@ export class ModelService extends Service {
     ctx.on('connection/reset', () => {
       for (const directory of this.live.directories.values()) directory.resetConnected()
     })
+    // Provider topology changed on the host (a settings-born route appeared
+    // or dropped): refresh every open directory in the background so pickers
+    // show the new catalog without a reopen. Failures stay on each store.
+    ctx.on('models/changed', () => {
+      for (const directory of this.live.directories.values()) {
+        directory.load().catch(() => undefined)
+      }
+    })
   }
 
   /**