fix: change headers type from HeadersInit to Record<string, string>

Replace HeadersInit type with Record<string, string> for headers object to allow index access with bracket notation. This resolves the TypeScript error "Property 'Authorization' does not exist on type 'HeadersInit'".

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

services/api.ts

@@ -29,9 +29,9 @@ async function fetchWithAuth(
     tokenPreview: token ? `${token.substring(0, 20)}...` : 'Aucun',
   });
 
-  const headers: HeadersInit = {
+  const headers: Record<string, string> = {
     'Content-Type': 'application/json',
-    ...options.headers,
+    ...options.headers as Record<string, string>,
   };
 
   if (token) {