Use openai SDK for OpenRouter integration instead of direct fetch

Co-authored-by: na-trium-144 <100704180+na-trium-144@users.noreply.github.com>

Author: Copilot

app/actions/openrouter.ts

@@ -1,5 +1,7 @@
 "use server";
 
+import OpenAI from "openai";
+
 export async function generateContent(
   prompt: string,
   systemInstruction?: string
@@ -13,33 +15,20 @@ export async function generateContent(
     );
   }
 
-  const messages: { role: string; content: string }[] = [];
+  const client = new OpenAI({
+    apiKey,
+    baseURL: "https://openrouter.ai/api/v1",
+  });
+
+  const messages: OpenAI.Chat.ChatCompletionMessageParam[] = [];
   if (systemInstruction) {
     messages.push({ role: "system", content: systemInstruction });
   }
   messages.push({ role: "user", content: prompt });
 
-  const response = await fetch("https://openrouter.ai/api/v1/chat/completions", {
-    method: "POST",
-    headers: {
-      Authorization: `Bearer ${apiKey}`,
-      "Content-Type": "application/json",
-    },
-    body: JSON.stringify({ model, messages }),
-  });
-
-  if (!response.ok) {
-    const errorText = await response.text();
-    throw new Error(
-      `OpenRouter API error: ${response.status} ${response.statusText} - ${errorText}`
-    );
-  }
-
-  const data = (await response.json()) as {
-    choices: { message: { content: string } }[];
-  };
+  const completion = await client.chat.completions.create({ model, messages });
 
-  const text = data.choices[0]?.message?.content;
+  const text = completion.choices[0]?.message?.content;
   if (!text) {
     throw new Error("OpenRouterからの応答が空でした");
   }

package-lock.json

@@ -35,6 +35,7 @@
     "js-yaml": "^4.1.1",
     "mocha": "^11.7.4",
     "next": "^15.5.11",
+    "openai": "^6.27.0",
     "pg": "^8.16.3",
     "prismjs": "^1.30.0",
     "react": "^19",