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.

app/src/components/SettingsPanel.tsx

@@ -24,7 +24,9 @@ export function SettingsPanel() {
     <div className="panel" onClick={() => setShowSettings(false)}>
       <div className="panel-inner" onClick={(e) => e.stopPropagation()}>
         <div className="panel-head">
-          <h2>Settings</h2>
+          <h2>
+            Settings <span className="build-date">{__BUILD_DATE__}</span>
+          </h2>
           <button className="icon-btn" onClick={() => setShowSettings(false)}>
             <CloseIcon width={20} height={20} />
           </button>

app/src/styles.css

@@ -1087,6 +1087,13 @@ select:focus {
   margin: 0;
   font-size: 18px;
 }
+
+.panel-head .build-date {
+  font-size: 11.5px;
+  font-weight: 400;
+  color: var(--text-faint);
+  margin-left: 6px;
+}
 .panel-head .icon-btn {
   margin-left: auto;
 }

app/src/vite-env.d.ts

@@ -0,0 +1,4 @@
+/// <reference types="vite/client" />
+
+/** Injected by `vite.config.ts` via `define` — set to the build/dev-server start time. */
+declare const __BUILD_DATE__: string;

app/vite.config.ts

@@ -4,6 +4,13 @@ import { defineConfig, loadEnv, type Plugin } from "vite";
 import react from "@vitejs/plugin-react";
 import { VitePWA } from "vite-plugin-pwa";
 
+/** `yyyy-mm-dd_hh:mm` timestamp of this build/dev-server start, shown in the UI. */
+function buildDateString(): string {
+  const d = new Date();
+  const pad = (n: number) => String(n).padStart(2, "0");
+  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}_${pad(d.getHours())}:${pad(d.getMinutes())}`;
+}
+
 /** Emits the repo's LICENSE file into the build output. */
 function licensePlugin(): Plugin {
   return {
@@ -27,6 +34,9 @@ export default defineConfig(({ mode }) => {
   const target = env.HERMES_DEV_TARGET;
 
   return {
+    define: {
+      __BUILD_DATE__: JSON.stringify(buildDateString()),
+    },
     server: {
       port: 5173,
       proxy: target