feat: switch to latest gemini 3.5 flash lite models

backend/server.js

@@ -338,7 +338,7 @@ app.post('/api/sparkplug/extract', authenticate, upload.single('file'), async (r
 
     // Call Gemini to extract prompt
     const genAI = new GoogleGenerativeAI(geminiKey);
-    const model = genAI.getGenerativeModel({ model: "gemini-1.5-flash-8b" });
+    const model = genAI.getGenerativeModel({ model: "gemini-3.5-flash-lite" });
 
     const prompt = `
       You are an expert product designer. Read the following text from a product spec PDF and create a highly detailed, concise visual design prompt for an image generation AI.
@@ -373,7 +373,7 @@ app.post('/api/sparkplug/generate-images', authenticate, async (req, res) => {
     if (!apiKey) return res.status(400).json({ error: 'Nano Banana (Gemini) API key missing' });
 
     // We will use axios to call the Gemini Imagen REST API
-    const baseUrl = 'https://generativelanguage.googleapis.com/v1beta/models/imagen-3.0-generate-001:predict';
+    const baseUrl = 'https://generativelanguage.googleapis.com/v1beta/models/gemini-3.1-flash-lite-image:predict';
     
     const views = ['Front view', 'Back view', 'Left side view', 'Right side view'];
     const imageUrls = [];