feat: add custom OpenAI endpoint and custom model support

- Added OPENAI_ENDPOINT in .env.local and retained default keys.
- Updated providers.ts to use baseURL from OPENAI_ENDPOINT.
- Conditionally override model names with OPENAI_MODEL when a custom endpoint is set.
- Supports custom provider configuration for local models via environment variables.

.gitignore

@@ -39,3 +39,4 @@ yarn-error.log*
 # Misc
 .DS_Store
 *.pem
+bun.lockb

src/ai/providers.ts

@@ -1,26 +1,44 @@
-import { createOpenAI } from '@ai-sdk/openai';
+import { createOpenAI, type OpenAIProviderSettings } from '@ai-sdk/openai';
 import { getEncoding } from 'js-tiktoken';
 
 import { RecursiveCharacterTextSplitter } from './text-splitter';
 
-// Providers
+interface CustomOpenAIProviderSettings extends OpenAIProviderSettings {
+  baseURL?: string;
+}
 
+// Providers
 const openai = createOpenAI({
   apiKey: process.env.OPENAI_KEY!,
-});
+  baseURL: process.env.OPENAI_ENDPOINT || 'https://api.openai.com/v1',
+} as CustomOpenAIProviderSettings);
+
+const isCustomEndpoint =
+  process.env.OPENAI_ENDPOINT &&
+  process.env.OPENAI_ENDPOINT !== 'https://api.openai.com/v1';
+const customModel = process.env.OPENAI_MODEL;
 
 // Models
 
-export const gpt4Model = openai('gpt-4o', {
-  structuredOutputs: true,
-});
-export const gpt4MiniModel = openai('gpt-4o-mini', {
-  structuredOutputs: true,
-});
-export const o3MiniModel = openai('o3-mini', {
-  reasoningEffort: 'medium',
-  structuredOutputs: true,
-});
+export const gpt4Model = openai(
+  isCustomEndpoint && customModel ? customModel : 'gpt-4o',
+  {
+    structuredOutputs: true,
+  },
+);
+export const gpt4MiniModel = openai(
+  isCustomEndpoint && customModel ? customModel : 'gpt-4o-mini',
+  {
+    structuredOutputs: true,
+  },
+);
+export const o3MiniModel = openai(
+  isCustomEndpoint && customModel ? customModel : 'o3-mini',
+  {
+    reasoningEffort: 'medium',
+    structuredOutputs: true,
+  },
+);
 
 const MinChunkSize = 140;
 const encoder = getEncoding('o200k_base');