fix(web): align mobile onboarding header

apps/web/src/routes/-chatIndexTitlebar.test.ts

@@ -0,0 +1,20 @@
+// @effect-diagnostics nodeBuiltinImport:off - Regression coverage compares the onboarding header with the shared titlebar contract.
+import * as NodeFS from "node:fs";
+
+import { describe, expect, it } from "vite-plus/test";
+
+describe("hosted static onboarding header", () => {
+  it("uses the shared workspace topbar geometry", () => {
+    const routeSource = NodeFS.readFileSync(new URL("./_chat.index.tsx", import.meta.url), "utf8");
+    const onboardingStart = routeSource.indexOf("function HostedStaticOnboardingState()");
+    const onboardingEnd = routeSource.indexOf('<Empty className="flex-1">', onboardingStart);
+
+    expect(onboardingStart).toBeGreaterThanOrEqual(0);
+    expect(onboardingEnd).toBeGreaterThan(onboardingStart);
+
+    const onboardingHeader = routeSource.slice(onboardingStart, onboardingEnd);
+
+    expect(onboardingHeader).toContain("workspace-topbar");
+    expect(onboardingHeader).not.toMatch(/(?:^|\s)(?:[\w-]+:)*py-/);
+  });
+});

apps/web/src/routes/_chat.index.tsx

@@ -145,7 +145,7 @@ function HostedStaticOnboardingState() {
       <div className="flex min-h-0 min-w-0 flex-1 flex-col overflow-x-hidden bg-background">
         <header
           className={cn(
-            "border-b border-border px-3 py-2 transition-[padding-left] duration-200 ease-linear motion-reduce:transition-none sm:px-5 sm:py-3",
+            "workspace-topbar border-b border-border px-3 transition-[padding-left] duration-200 ease-linear motion-reduce:transition-none sm:px-5",
             COLLAPSED_SIDEBAR_TITLEBAR_INSET_CLASS,
           )}
         >