feat: add support for GitHub Models provider

- Introduced environment variable CLAUDE_CODE_USE_GITHUB to enable GitHub Models.
- Added checks for GITHUB_TOKEN or GH_TOKEN for authentication.
- Updated base URL handling to include GitHub Models default.
- Enhanced provider detection and error handling for GitHub Models.
- Updated relevant functions and components to accommodate the new provider.

src/services/api/client.ts

@@ -154,7 +154,10 @@ export async function getAnthropicClient({
       fetch: resolvedFetch,
     }),
   }
-  if (isEnvTruthy(process.env.CLAUDE_CODE_USE_OPENAI)) {
+  if (
+    isEnvTruthy(process.env.CLAUDE_CODE_USE_OPENAI) ||
+    isEnvTruthy(process.env.CLAUDE_CODE_USE_GITHUB)
+  ) {
     const { createOpenAIShimClient } = await import('./openaiShim.js')
     return createOpenAIShimClient({
       defaultHeaders,