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>

components/shared/region-select.tsx

@@ -71,10 +71,10 @@ export default function RegionSelect({
           ))}
         </select>
       </div>
-      {cityOptional && provinceCode && (
+      {cityOptional && provinceCode && location && (
         <p className="text-xs text-muted-foreground">
-          城市可不选，默认使用省份经度；已选：
-          {location ? `${location.name}（${location.longitude}°）` : "—"}
+          城市可选；未选城市时使用省份经度。当前：
+          {location.name}（{location.longitude}°）
         </p>
       )}
     </div>