Add Auto Dark Mode support

server/dark.ts

@@ -0,0 +1,4 @@
+export function detect_darkmode() {
+    return window.matchMedia &&
+        window.matchMedia("(prefers-color-scheme: dark)").matches;
+}

server/parse.ts

@@ -11,3 +11,13 @@ export function parse_bool<T extends boolean | null>(
         return n !== 0;
     }
 }
+
+export function parse_int<T extends number | null>(
+    value: string | null,
+    def: T,
+): number | T {
+    if (value === null) return def;
+    const n = parseInt(value);
+    if (isNaN(n)) return def;
+    return n;
+}