fix: use gemini-3.1-flash-image and generateContent API for image generation

backend/server.js

@@ -370,7 +370,7 @@ app.post('/api/sparkplug/extract', authenticate, upload.single('file'), async (r
   }
 });
 
-// 2. Generate Images (Gemini Imagen 3)
+// 2. Generate Images (Gemini 3.1 Flash Image)
 app.post('/api/sparkplug/generate-images', authenticate, async (req, res) => {
   const { prompt } = req.body;
   if (!prompt) return res.status(400).json({ error: 'No prompt provided' });
@@ -380,8 +380,8 @@ app.post('/api/sparkplug/generate-images', authenticate, async (req, res) => {
     const apiKey = keys.GEMINI_API_KEY || keys.NANO_BANANA_API_KEY;
     if (!apiKey) return res.status(400).json({ error: 'Gemini API key missing' });
 
-    // Use the standard Gemini Imagen 3 API
-    const baseUrl = 'https://generativelanguage.googleapis.com/v1beta/models/imagen-3.0-generate-images:predict';
+    // Use the Gemini 3.1 Flash Image API
+    const baseUrl = 'https://generativelanguage.googleapis.com/v1beta/models/gemini-3.1-flash-image:generateContent';
     
     const views = ['Front view', 'Back view', 'Left side view', 'Right side view'];
 
@@ -390,12 +390,15 @@ app.post('/api/sparkplug/generate-images', authenticate, async (req, res) => {
       const fullPrompt = `${prompt}. ${view}, isolated on a pure white background, studio lighting.`;
       
       const payload = {
-        instances: [
-          { prompt: fullPrompt }
+        contents: [
+          {
+            parts: [
+              { text: fullPrompt }
+            ]
+          }
         ],
-        parameters: {
-          sampleCount: 1,
-          aspectRatio: "1:1"
+        generationConfig: {
+          responseModalities: ["IMAGE"]
         }
       };
 
@@ -404,8 +407,18 @@ app.post('/api/sparkplug/generate-images', authenticate, async (req, res) => {
       });
 
       let base64Image = null;
-      if (response.data && response.data.predictions && response.data.predictions.length > 0) {
-        base64Image = response.data.predictions[0].bytesBase64Encoded;
+      let mimeType = 'image/jpeg';
+      
+      // Extract from standard Gemini generateContent response
+      const candidate = response.data?.candidates?.[0];
+      if (candidate?.content?.parts) {
+        for (const part of candidate.content.parts) {
+          if (part.inlineData && part.inlineData.data) {
+            base64Image = part.inlineData.data;
+            mimeType = part.inlineData.mimeType || 'image/jpeg';
+            break;
+          }
+        }
       }
 
       if (!base64Image) {
@@ -413,8 +426,8 @@ app.post('/api/sparkplug/generate-images', authenticate, async (req, res) => {
       }
 
       const buffer = Buffer.from(base64Image, 'base64');
-      
-      const filename = `sparkplug-${req.user.id}-${Date.now()}-${index}.png`;
+      const ext = mimeType === 'image/png' ? 'png' : 'jpg';
+      const filename = `sparkplug-${req.user.id}-${Date.now()}-${index}.${ext}`;
       const filepath = path.join(uploadsDir, filename);
       fs.writeFileSync(filepath, buffer);