refactor(agent): runAgent uses Agent upstreams only; deprecate legacy settings.pi fields

pi.provider / baseUrl / model / thinkingLevel / apiKeySecretRef are now
DEPRECATED_SETTINGS_FIELDS: kept in the schema for stored JSON, dropped
from PATCH /settings and from the settings sections, never read by the
server. runAgent fails with a clear message when no upstream is set.
The agent demo gate checks the default upstream provider; e2e seeds a
fake upstream as default. OpenAPI summaries say Agent upstream.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/components/settings/pi-upstreams.tsx

@@ -10,7 +10,6 @@ import {
   useRemovePiUpstream,
   useUpdatePiUpstream,
 } from "~/api/pi.ts";
-import { useSettings } from "~/api/settings.ts";
 import { ConfirmDialog } from "~/components/console/confirm-dialog.tsx";
 import { DataTable } from "~/components/console/data-table.tsx";
 import { DetailSection, DetailSheet } from "~/components/console/detail-sheet.tsx";
@@ -39,12 +38,10 @@ import { SettingsBlock } from "./settings-block.tsx";
 export function PiUpstreamsBlock() {
   const list = usePiUpstreams();
   const providers = usePiProviders(false);
-  const settings = useSettings();
   const [wizard, setWizard] = useState(false);
   const [openId, setOpenId] = useState<string | null>(null);
   const open = list.data?.items.find((u) => u.id === openId) ?? null;
   const pv = providers.data?.providers;
-  const legacy = settings.data?.pi.provider;
 
   return (
     <SettingsBlock
@@ -67,10 +64,7 @@ export function PiUpstreamsBlock() {
         error={list.error}
         onRetry={() => list.refetch()}
         onRowClick={(r) => setOpenId(r.id)}
-        empty={{
-          title: "还没有上游",
-          description: legacy ? `没有上游时按旧设置运行(provider:${legacy})。` : undefined,
-        }}
+        empty={{ title: "还没有上游" }}
         columns={[
           {
             key: "name",