Implement three divination modes, learn pages, and PM2 deploy on port 3130.

Add liuyao/bazi/combined flows with shared calc and AI infrastructure, 64-gua learn routes, and update Ubuntu PM2 deployment docs for port 3130.

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

components/header.tsx

@@ -1,15 +1,53 @@
+"use client";
+import Link from "next/link";
+import { usePathname } from "next/navigation";
 import { ChatGPT } from "@/components/svg";
 import { ModeToggle } from "@/components/mode-toggle";
 
+const NAV_ITEMS = [
+  { href: "/learn", label: "易经学习" },
+  { href: "/liuyao", label: "六爻算卦" },
+  { href: "/bazi", label: "生辰八字" },
+  { href: "/combined", label: "综合测算" },
+];
+
+function NavLink({ href, label }: { href: string; label: string }) {
+  const pathname = usePathname();
+  const active =
+    href === "/"
+      ? pathname === "/"
+      : pathname === href || pathname.startsWith(`${href}/`);
+
+  return (
+    <Link
+      href={href}
+      className={`whitespace-nowrap text-sm transition-colors ${
+        active
+          ? "font-medium text-foreground"
+          : "text-muted-foreground hover:text-foreground"
+      }`}
+    >
+      {label}
+    </Link>
+  );
+}
+
 export default function Header() {
   return (
-    <header className="h-14 bg-secondary py-2 shadow">
-      <div className="mx-auto flex h-full w-full items-center justify-center sm:max-w-md sm:justify-between md:max-w-2xl">
-        <div className="flex gap-2">
+    <header className="bg-secondary py-2 shadow">
+      <div className="mx-auto flex w-full max-w-4xl flex-col gap-2 px-4 sm:flex-row sm:items-center sm:justify-between">
+        <Link href="/" className="flex items-center justify-center gap-2 sm:justify-start">
           <ChatGPT />
-          <span>知命阁</span>
+          <span className="font-medium">知命阁</span>
+        </Link>
+        <nav className="flex flex-wrap items-center justify-center gap-x-4 gap-y-1">
+          {NAV_ITEMS.map((item) => (
+            <NavLink key={item.href} {...item} />
+          ))}
+        </nav>
+        <div className="flex justify-center sm:justify-end">
+          <ModeToggle />
         </div>
-        <ModeToggle />
       </div>
     </header>
   );