fix(panel): reactive system theme detection

panel/index.html

@@ -6,8 +6,7 @@
     <title>Felis · Control Panel</title>
     <script>
       try {
-        const theme = localStorage.getItem("felis-theme") || "system";
-        const dark = theme === "dark" || (theme === "system" && window.matchMedia("(prefers-color-scheme: dark)").matches);
+        const dark = window.matchMedia("(prefers-color-scheme: dark)").matches;
         if (dark) {
           document.documentElement.classList.add("dark");
         } else {