feat: add S3 config validation and improve error messages in STT endpoint

apps/api/src/stt.ts

@@ -12,7 +12,13 @@ router.post('/', async (req, res) => {
       return res.status(400).json({ error: 'bucket (or env S3_BUCKET) and key are required' });
     }
     if (!process.env.OPENAI_API_KEY) {
-      return res.status(500).json({ error: 'OPENAI_API_KEY not configured' });
+      console.error('STT failed: missing OPENAI_API_KEY');
+      return res.status(500).json({ error: 'Transcription not configured' });
+    }
+    const { S3_ENDPOINT, S3_ACCESS_KEY, S3_SECRET_KEY } = process.env;
+    if (!S3_ENDPOINT || !S3_ACCESS_KEY || !S3_SECRET_KEY) {
+      console.error('STT failed: missing S3 config (S3_ENDPOINT/S3_ACCESS_KEY/S3_SECRET_KEY)');
+      return res.status(500).json({ error: 'Object storage not configured' });
     }
 
     const { buffer, contentType } = await downloadObject({ bucket, key });