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/ai/stream.ts

@@ -18,6 +18,10 @@ export async function streamAIResponse(
   system: string,
   user: string,
 ): Promise<{ data?: ReturnType<typeof createStreamableValue<string>>["value"]; error?: string }> {
+  if (!process.env.OPENAI_API_KEY?.trim()) {
+    return { error: "未配置 OPENAI_API_KEY，请在 .env.local 或 Docker env_file 中设置" };
+  }
+
   const stream = createStreamableValue<string>();
 
   try {