refactor: follow system color scheme via matchMedia listener

static/theme.ts

@@ -1,62 +1,20 @@
 type Theme = "light" | "dark";
 
-const STORAGE_KEY = "theme";
-
-const getLocalStorage = (): Storage | null => {
-  try {
-    return window.localStorage;
-  } catch {
-    return null;
-  }
-};
+const colorSchemeQuery = window.matchMedia?.("(prefers-color-scheme: dark)") ?? null;
 
 const getPreferredTheme = (): Theme => {
-  const prefersDark = window.matchMedia?.("(prefers-color-scheme: dark)")?.matches ?? false;
+  const prefersDark = colorSchemeQuery?.matches ?? false;
   return prefersDark ? "dark" : "light";
 };
 
-const normalizeTheme = (raw: string | null): Theme | null => {
-  if (raw === "light" || raw === "dark") return raw;
-  return null;
-};
-
-const getSavedTheme = (): Theme => {
-  const storage = getLocalStorage();
-  const fromStorage = normalizeTheme(storage?.getItem(STORAGE_KEY) ?? null);
-  if (fromStorage) return fromStorage;
-
-  return getPreferredTheme();
-};
-
 const applyTheme = (theme: Theme): void => {
   document.documentElement.setAttribute("data-theme", theme);
   document.documentElement.style.colorScheme = theme;
-  const storage = getLocalStorage();
-  try {
-    storage?.setItem(STORAGE_KEY, theme);
-  } catch {
-    // ignore
-  }
-};
-
-const cycleTheme = (): void => {
-  const current = getSavedTheme();
-  const next: Theme = current === "light" ? "dark" : "light";
-  applyTheme(next);
 };
 
 const initTheme = (): void => {
-  const saved = getSavedTheme();
-  applyTheme(saved);
-
-  // delegated click handler on theme buttons
-  document.addEventListener("click", (e) => {
-    const target = e.target;
-    if (!(target instanceof Element)) return;
-    const btn = target.closest("#theme-toggle, #footer-theme-toggle");
-    if (!(btn instanceof HTMLButtonElement)) return;
-    cycleTheme();
-  });
+  applyTheme(getPreferredTheme());
+  colorSchemeQuery?.addEventListener("change", () => applyTheme(getPreferredTheme()));
 };
 
 if (document.readyState === "loading") {