feat(web): set up React app shell with routing and layout

Adds react-router-dom with routes for ship list, dashboard, and rules pages.
Includes TopBar with navigation and mobile-first dark theme CSS.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/pages/RulesPage.tsx

@@ -0,0 +1,13 @@
+import TopBar from '../components/layout/TopBar';
+import PageContainer from '../components/layout/PageContainer';
+
+export default function RulesPage() {
+  return (
+    <>
+      <TopBar title="Battle Reference" />
+      <PageContainer>
+        <p style={{ color: 'var(--color-text-muted)' }}>Rules reference coming soon...</p>
+      </PageContainer>
+    </>
+  );
+}