Fix learn 404, coin animation, full regions, and AI key errors.

Use numeric /learn/{num} routes, register Tailwind coin animations with方孔铜钱 UI, expand to 34 provinces, and surface missing OPENAI_API_KEY clearly.

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

lib/content/zhouyi.ts

@@ -21,6 +21,21 @@ export async function listGuaMarks(
     .sort();
 }
 
+/** 序号 slug，如 "35" */
+export function guaNumFromMark(guaMark: string): string {
+  return guaMark.split(".")[0];
+}
+
+/** 由序号解析目录名，如 "35" → "35.火地晋" */
+export async function markFromNum(
+  num: string,
+  variant: LearnVariant = "traditional",
+): Promise<string | null> {
+  const padded = num.padStart(2, "0").slice(-2);
+  const marks = await listGuaMarks(variant);
+  return marks.find((m) => m.startsWith(`${padded}.`)) ?? null;
+}
+
 export async function readGuaMarkdown(guaMark: string): Promise<string> {
   const filePath = path.join(DOCS_ROOT, guaMark, "index.md");
   return fs.readFile(filePath, "utf-8");