fix(sessions): honor offline settings in background catalog refresher

The background model catalog refresher always requested a network refresh,
so sessiond fetched provider catalogs on a schedule even when the operator
set PI_OFFLINE or PI_WEB_OFFLINE. Before the refresher existed, those
settings made every runtime refresh local-only.

Add `offlineModeEnabled()` to the config module and inject the resulting
flag from sessiond's frozen daemon environment, so the refresher schedules
nothing and ignores auth-triggered requests in offline mode. The narrower
PI_SKIP_VERSION_CHECK / PI_WEB_SKIP_VERSION_CHECK keys are deliberately not
included: they only suppress release lookups.

src/config.test.ts

@@ -2,7 +2,7 @@ import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
 import { join } from "node:path";
 import { tmpdir } from "node:os";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
-import { DEFAULT_MAX_UPLOAD_BYTES, DEFAULT_UPLOADS_FOLDER, agentDirEnvSource, agentSessionDirEnvKeys, effectiveAgentConfig, effectivePiWebConfig, hasAgentDirEnvOverride, hasAgentSessionDirEnvOverride, loadPiWebConfig, maxUploadBytes, savePiWebConfig, spawnSessionsEnabled, subsessionsEnabled } from "./config.js";
+import { DEFAULT_MAX_UPLOAD_BYTES, DEFAULT_UPLOADS_FOLDER, agentDirEnvSource, agentSessionDirEnvKeys, effectiveAgentConfig, effectivePiWebConfig, hasAgentDirEnvOverride, hasAgentSessionDirEnvOverride, loadPiWebConfig, maxUploadBytes, offlineModeEnabled, savePiWebConfig, spawnSessionsEnabled, subsessionsEnabled } from "./config.js";
 
 let tempDir: string;
 let configPath: string;
@@ -233,6 +233,25 @@ describe("subsessionsEnabled", () => {
   });
 });
 
+describe("offlineModeEnabled", () => {
+  it("is off when no offline env var is set", () => {
+    expect(offlineModeEnabled({})).toBe(false);
+  });
+
+  it("treats an empty value as unset", () => {
+    expect(offlineModeEnabled({ PI_OFFLINE: "", PI_WEB_OFFLINE: "" })).toBe(false);
+  });
+
+  it("is on when either offline key has a value", () => {
+    expect(offlineModeEnabled({ PI_OFFLINE: "1" })).toBe(true);
+    expect(offlineModeEnabled({ PI_WEB_OFFLINE: "anything" })).toBe(true);
+  });
+
+  it("ignores the narrower skip-version-check keys", () => {
+    expect(offlineModeEnabled({ PI_SKIP_VERSION_CHECK: "1", PI_WEB_SKIP_VERSION_CHECK: "1" })).toBe(false);
+  });
+});
+
 function testOptions(): { env: NodeJS.ProcessEnv } {
   return { env: { PI_WEB_CONFIG: configPath } };
 }