feat(frontend): add dark mode option (#34)

Resolves #32

Reviewed-on: #34

frontend/index.html

@@ -9,6 +9,20 @@
     <link href="https://fonts.googleapis.com/css2?family=Newsreader:wght@100;200;300;400;500;600;700&family=IBM+Plex+Sans:wght@100;200;300;400;500;600;700&family=IBM+Plex+Mono:wght@100;200;300;400;500;600;700&display=swap" rel="stylesheet">
 
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <script>
+      // Apply the stored theme before first paint so a dark session never
+      // flashes light. Mirrors the logic in src/theme/ThemeProvider.tsx.
+      (function () {
+        try {
+          var stored = localStorage.getItem("theme");
+          var dark = stored === "dark" ||
+            (stored !== "light" && window.matchMedia("(prefers-color-scheme: dark)").matches);
+          document.documentElement.dataset.theme = dark ? "dark" : "light";
+        } catch (e) {
+          document.documentElement.dataset.theme = "light";
+        }
+      })();
+    </script>
     <script src="/env-config.js"></script>
     <title>The VoD System</title>
   </head>