Add Gemini 2.0 Flash Thinking model support

- Add Google Gemini 2.0 Flash Thinking as an available model
- Free tier available with extended thinking capabilities
- Add GOOGLE_API_KEY to .env.example for easy setup
- Users can get a free API key at https://aistudio.google.com/apikey

Author: camilleislasse

chat-client/.env.example

@@ -1,3 +1,4 @@
 # API Keys (Optional - can also be set via UI settings)
 ANTHROPIC_API_KEY=sk-ant-...
 OPENAI_API_KEY=sk-...
+GOOGLE_API_KEY=AIza...

chat-client/ai/providers.ts

@@ -1,10 +1,11 @@
 import { createOpenAI } from "@ai-sdk/openai";
 import { createAnthropic } from "@ai-sdk/anthropic";
+import { createGoogleGenerativeAI } from "@ai-sdk/google";
 
-import { 
-  customProvider, 
-  wrapLanguageModel, 
-  extractReasoningMiddleware 
+import {
+  customProvider,
+  wrapLanguageModel,
+  extractReasoningMiddleware
 } from "ai";
 
 export interface ModelInfo {
@@ -25,12 +26,12 @@ const getApiKey = (key: string): string | undefined => {
   if (process.env[key]) {
     return process.env[key] || undefined;
   }
-  
+
   // Fall back to localStorage if available
   if (typeof window !== 'undefined') {
     return window.localStorage.getItem(key) || undefined;
   }
-  
+
   return undefined;
 };
 
@@ -43,12 +44,16 @@ const anthropicClient = createAnthropic({
   apiKey: getApiKey('ANTHROPIC_API_KEY'),
 });
 
+const googleClient = createGoogleGenerativeAI({
+  apiKey: getApiKey('GOOGLE_API_KEY'),
+});
 
 // const xaiClient = createXai({
 //   apiKey: getApiKey('XAI_API_KEY'),
 // });
 
 const languageModels = {
+  "gemini-2-flash-thinking": googleClient("gemini-2.0-flash-thinking-exp-01-21"),
   "gpt-5": openaiClient("gpt-5-2025-08-07"),
   "claude-4-sonnet": anthropicClient('claude-sonnet-4-20250514'),
   // "qwen-qwq": wrapLanguageModel(
@@ -61,6 +66,13 @@ const languageModels = {
 };
 
 export const modelDetails: Record<keyof typeof languageModels, ModelInfo> = {
+  "gemini-2-flash-thinking": {
+    provider: "Google",
+    name: "Gemini 2.0 Flash Thinking",
+    description: "Google's reasoning model with extended thinking capabilities. Free tier available.",
+    apiVersion: "gemini-2.0-flash-thinking-exp-01-21",
+    capabilities: ["Deep Reasoning", "Thinking", "Free", "Agentic"]
+  },
   "gpt-5": {
     provider: "OpenAI",
     name: "GPT-5",