Fix Docker build by splitting client-safe gua utils from fs-based content loader.

Client components were importing zhouyi.ts which pulled in fs/promises; move pure helpers to gua-utils.ts and mark zhouyi.ts server-only.

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

components/learn/gua-footer.tsx

@@ -1,7 +1,7 @@
 import Link from "next/link";
 import { Button } from "@/components/ui/button";
 import { Sparkles } from "lucide-react";
-import { guaNumFromMark } from "@/lib/content/zhouyi";
+import { guaNumFromMark } from "@/lib/content/gua-utils";
 
 export default function GuaFooter({
   guaMark,

components/learn/markdown-content.tsx

@@ -1,6 +1,6 @@
 import Link from "next/link";
 import Markdown from "react-markdown";
-import type { LearnVariant } from "@/lib/content/zhouyi";
+import type { LearnVariant } from "@/lib/content/gua-utils";
 
 function resolveLearnHref(
   href: string | undefined,

components/result.tsx

@@ -1,6 +1,6 @@
 import React from "react";
 import Link from "next/link";
-import { guaNumFromMark } from "@/lib/content/zhouyi";
+import { guaNumFromMark } from "@/lib/content/gua-utils";
 
 export interface ResultObj {
   guaTitle: string;