Show build date next to "Settings" heading

Inject a yyyy-mm-dd_hh:mm timestamp at build time via Vite's `define`
(app/vite.config.ts: __BUILD_DATE__, computed fresh on every
`vite build`/`vite dev` invocation) and render it next to the
Settings panel's title, so it's easy to tell which build is deployed.

- app/vite.config.ts: buildDateString() + define.__BUILD_DATE__
- app/src/vite-env.d.ts: ambient declaration for the injected constant
- app/src/components/SettingsPanel.tsx: render it next to "Settings"
- app/src/styles.css: .build-date styling

Rebuilt and redeployed to the repo root.

index.html

@@ -13,8 +13,8 @@
     <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
     <meta name="apple-mobile-web-app-title" content="Hermes" />
     <title>Hermes</title>
-    <script type="module" crossorigin src="/assets/index-SBr79e_P.js"></script>
-    <link rel="stylesheet" crossorigin href="/assets/index-CWSassUi.css">
+    <script type="module" crossorigin src="/assets/index-BFnujVjw.js"></script>
+    <link rel="stylesheet" crossorigin href="/assets/index-BQJys9C3.css">
   <link rel="manifest" href="/manifest.webmanifest"></head>
   <body>
     <div id="root"></div>