refactor(ai-event): migrate to OpenRouter chat.send API

Replace the deprecated callModel / getText pattern with the chat.send
method and extract the response content via extractContentFromChatResponse.
This aligns with the current OpenRouter SDK interface.

src/app/api/ai-event/route.ts

@@ -39,13 +39,17 @@ Rules:
 `;
 
 const callTextOnly = async (systemPrompt: string, prompt: string) => {
-	const result = openRouterClient.callModel({
-		model: MODEL,
-		instructions: systemPrompt,
-		input: prompt,
+	const response = await openRouterClient.chat.send({
+		chatRequest: {
+			model: MODEL,
+			messages: [
+				{ role: "system", content: systemPrompt },
+				{ role: "user", content: prompt },
+			],
+		},
 	});
 
-	const rawResponse = await result.getText();
+	const rawResponse = extractContentFromChatResponse(response);
 	return { rawResponse };
 };