feat(FN-3434): add Claude OAuth credential interop with verification and st

This merge lands four major features: the desktop app gains shell onboarding with remote mode support via a new `DesktopModeChooser` and `shell-settings` module (FN-3399); the dashboard gains full archived insights support with the `InsightsView` redesign and `useInsights` hook overhaul (FN-3315); C

Fusion-Task-Id: FN-3434

packages/engine/src/__tests__/auth-storage.test.ts

@@ -139,6 +139,32 @@ describe("createFusionAuthStorage", () => {
     });
   });
 
+  it("reads valid Claude OAuth credentials from Claude credential files", async () => {
+    const claudeDir = join(homeDir, ".claude");
+    mkdirSync(claudeDir, { recursive: true });
+
+    writeFileSync(
+      join(claudeDir, ".credentials.json"),
+      JSON.stringify({
+        claudeAiOauth: {
+          accessToken: "claude-access-token",
+          refreshToken: "claude-refresh-token",
+          expiresAt: Date.now() + 3_600_000,
+        },
+      }),
+    );
+
+    const authStorage = createFusionAuthStorage();
+
+    expect(await authStorage.getApiKey("anthropic")).toBe("claude-access-token");
+    expect(authStorage.get("anthropic")).toEqual({
+      type: "oauth",
+      access: "claude-access-token",
+      refresh: "claude-refresh-token",
+      expires: expect.any(Number),
+    });
+  });
+
   it("hydrates newer Codex CLI OAuth credentials into Fusion auth on reload", async () => {
     const fusionAgentDir = join(homeDir, ".fusion", "agent");
     const codexDir = join(homeDir, ".codex");

packages/engine/src/auth-storage.ts

@@ -3,6 +3,7 @@ import { homedir } from "node:os";
 import { join } from "node:path";
 import {
   choosePreferredStoredCredential,
+  getClaudeCodeCredentialPaths,
   getCodexCliAuthPath,
   readStoredCredentialsFromAuthFile,
   shouldHydrateStoredCredential,
@@ -38,6 +39,7 @@ function getSupplementalAuthPaths(home = getHomeDir()): string[] {
   return [
     ...getLegacyAuthPaths(home),
     getCodexCliAuthPath(home),
+    ...getClaudeCodeCredentialPaths(home),
   ];
 }