feat(web): PageShell narrow variant for dense single-column tabs

Adds a 'narrow' prop that wraps the body in 'max-w-2xl mx-auto'
while keeping the header chrome at the standard 5xl. Settings is
the first consumer — its rows are dense text and look adrift at
full width. The header still aligns with the other tabs so the
title position stays consistent.

Covered by 2 SSR tests (narrow path adds the inner wrapper, default
path doesn't).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/app/settings/page.tsx

@@ -8,7 +8,7 @@ import { PageShell } from "@/components/page-shell";
 export default async function SettingsPage() {
   const op = await getSeededOperator();
   return (
-    <PageShell title="Settings">
+    <PageShell title="Settings" narrow>
       <Card>
         <CardHeader>
           <CardTitle>Operator</CardTitle>

apps/web/src/components/page-shell.test.tsx

@@ -56,4 +56,25 @@ describe("PageShell", () => {
     expect(html).toContain("Settings");
     expect(html).toContain("just a card");
   });
+
+  it("constrains the body to max-w-2xl when narrow is set", () => {
+    const html = renderToStaticMarkup(
+      <PageShell title="Settings" narrow>
+        <p>card</p>
+      </PageShell>,
+    );
+    // Outer chrome stays at 5xl so the header keeps its alignment;
+    // an inner wrapper drops the body to 2xl.
+    expect(html).toMatch(/max-w-5xl/);
+    expect(html).toMatch(/max-w-2xl mx-auto/);
+  });
+
+  it("does NOT add the inner narrow wrapper by default", () => {
+    const html = renderToStaticMarkup(
+      <PageShell title="Reminders">
+        <p>list</p>
+      </PageShell>,
+    );
+    expect(html).not.toMatch(/max-w-2xl/);
+  });
 });

apps/web/src/components/page-shell.tsx

@@ -8,6 +8,10 @@ interface PageShellProps {
    *  button. When omitted, the header row collapses to just the H1
    *  on desktop and renders nothing on mobile. */
   action?: ReactNode;
+  /** Constrain the body to `max-w-2xl` for dense, single-column
+   *  content (Settings, etc). The header stays at the standard
+   *  5xl chrome so the title aligns with other tabs. */
+  narrow?: boolean;
   children: ReactNode;
 }
 
@@ -18,7 +22,7 @@ interface PageShellProps {
  * this so the header pattern stays consistent without each page
  * repeating the same wrapper markup.
  */
-export function PageShell({ title, action, children }: PageShellProps) {
+export function PageShell({ title, action, narrow, children }: PageShellProps) {
   return (
     <div className="px-4 py-6 sm:px-6 sm:py-8 max-w-5xl mx-auto space-y-6">
       <div className="flex items-center justify-end sm:justify-between gap-4">
@@ -27,7 +31,11 @@ export function PageShell({ title, action, children }: PageShellProps) {
         </h1>
         {action}
       </div>
-      {children}
+      {narrow ? (
+        <div className="max-w-2xl mx-auto space-y-6">{children}</div>
+      ) : (
+        children
+      )}
     </div>
   );
 }