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>

app/learn/page.tsx

@@ -2,7 +2,7 @@ import Link from "next/link";
 import PageShell from "@/components/page-shell";
 import {
   getGuaName,
-  getGuaNumber,
+  guaNumFromMark,
   listGuaMarks,
 } from "@/lib/content/zhouyi";
 
@@ -35,11 +35,11 @@ export default async function LearnPage() {
             {guaMarks.map((mark) => (
               <tr key={mark} className="border-t">
                 <td className="px-4 py-2 font-mono text-muted-foreground">
-                  {getGuaNumber(mark)}
+                  {guaNumFromMark(mark)}
                 </td>
                 <td className="px-4 py-2">
                   <Link
-                    href={`/learn/${encodeURIComponent(mark)}`}
+                    href={`/learn/${guaNumFromMark(mark)}`}
                     className="text-primary underline-offset-4 hover:underline"
                   >
                     {getGuaName(mark)}