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]>

packages/contracts/test/settings-sections.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from "vitest";
 import {
   DEFAULT_SETTINGS,
+  DEPRECATED_SETTINGS_FIELDS,
   SETTINGS_SECTIONS,
   SettingsSectionId,
   settingsSectionForLegacyTab,
@@ -11,8 +12,11 @@ describe("SETTINGS_SECTIONS", () => {
     expect(SETTINGS_SECTIONS.map((s) => s.id)).toEqual(SettingsSectionId.options);
   });
 
-  it("8 个存储 key 的每个字段恰好归属一个分区", () => {
-    const all = Object.entries(DEFAULT_SETTINGS).flatMap(([key, v]) => Object.keys(v).map((f) => `${key}.${f}`));
+  it("8 个存储 key 的每个字段(弃用字段除外)恰好归属一个分区", () => {
+    const deprecated = new Set<string>(DEPRECATED_SETTINGS_FIELDS);
+    const all = Object.entries(DEFAULT_SETTINGS)
+      .flatMap(([key, v]) => Object.keys(v).map((f) => `${key}.${f}`))
+      .filter((f) => !deprecated.has(f));
     const owned = SETTINGS_SECTIONS.flatMap((s) => s.fields);
     expect(new Set(owned).size).toBe(owned.length);
     expect([...owned].sort()).toEqual([...all].sort());