fix(gemini): implement model fallback system for reliability

src/services/gemini.ts

@@ -13,7 +13,19 @@ export async function generateGemini(prompt: string, systemPrompt: string): Prom
     throw new Error('Gemini API Key not found. Please set VITE_GEMINI_API_KEY in .env or GEMINI_API_KEY in localStorage.');
   }
 
-  const response = await fetch(`https://generativelanguage.googleapis.com/v1beta/models/gemini-pro:generateContent?key=${apiKey}`, {
+  // Model fallback list - based on March 2026 status
+  const modelOptions = [
+    'gemini-2.0-flash',
+    'gemini-1.5-flash',
+    'gemini-pro'
+  ];
+
+  let lastError: any = null;
+
+  for (const modelName of modelOptions) {
+    try {
+      console.log(`Trying Gemini model: ${modelName}...`);
+      const response = await fetch(`https://generativelanguage.googleapis.com/v1beta/models/${modelName}:generateContent?key=${apiKey}`, {
         method: 'POST',
         headers: {
           'Content-Type': 'application/json'
@@ -33,9 +45,19 @@ export async function generateGemini(prompt: string, systemPrompt: string): Prom
 
       if (!response.ok) {
         const errorData = await response.json().catch(() => ({}));
-    throw new Error(errorData.error?.message || 'Failed to generate text from Gemini API');
+        console.warn(`Model ${modelName} failed:`, errorData);
+        lastError = errorData;
+        continue; // Try next model
       }
 
       const data = await response.json();
+      console.log(`Successfully used model: ${modelName}`);
       return data.candidates[0].content.parts[0].text;
+    } catch (err) {
+      console.error(`Fetch error with ${modelName}:`, err);
+      lastError = err;
+    }
+  }
+
+  throw new Error(lastError?.error?.message || lastError?.message || 'All Gemini models failed. Check console for details.');
 }