Add OpenAI support, default to gpt-4o-mini

src/services/ai.ts

@@ -1,11 +1,19 @@
 import { ChatAnthropic } from '@langchain/anthropic';
+import { ChatOpenAI } from '@langchain/openai';
 import { ChatPromptTemplate } from '@langchain/core/prompts';
 import { StringOutputParser } from '@langchain/core/output_parsers';
 
 export type AIProvider = 'anthropic' | 'openai';
 
 // Get model based on provider
-function getModel(provider: AIProvider = 'anthropic') {
+function getModel(provider: AIProvider = 'openai') {
+  if (provider === 'openai') {
+    return new ChatOpenAI({
+      modelName: 'gpt-4o-mini',
+      openAIApiKey: process.env.OPENAI_API_KEY,
+    });
+  }
+  
   if (provider === 'anthropic') {
     return new ChatAnthropic({
       modelName: 'claude-sonnet-4-20250514',
@@ -13,8 +21,7 @@ function getModel(provider: AIProvider = 'anthropic') {
     });
   }
   
-  // Add OpenAI support later
-  throw new Error(`Provider ${provider} not yet supported`);
+  throw new Error(`Provider ${provider} not supported`);
 }
 
 // Email generation prompt