Add responsive content width for ultrawide while keeping 1080p layout.

Scale from 896px on 1080p up to 1440px on 3440px screens via viewport breakpoints in site-width.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/footer.tsx

@@ -1,10 +1,13 @@
 import React from "react";
 import { VERSION } from "@/lib/constant";
+import { SITE_WIDTH_INNER } from "@/components/layout/site-width";
 
 function Footer() {
   return (
     <footer className="relative z-10 flex items-center justify-center gap-1 border-t border-border/40 bg-card/70 py-4 text-xs text-muted-foreground/80">
-      <div className="mx-auto flex w-full max-w-4xl items-center justify-center gap-1 px-4 sm:px-6 lg:px-8">
+      <div
+        className={`${SITE_WIDTH_INNER} flex items-center justify-center gap-1`}
+      >
         <span className="italic">心诚则灵</span>
         <span className="text-muted-foreground/60">·</span>
         <span>知命阁 v{VERSION}</span>