feat: forward Authorization header from request to downstream

Prioritize Authorization header from incoming request over environment
variable, allowing per-request API key routing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/routes/ollama.ts

@@ -17,7 +17,7 @@ const ollamaRoutes: FastifyPluginAsync = async (server: FastifyInstance) => {
         return;
       }
 
-      const response = await forwardChatRequest(body);
+      const response = await forwardChatRequest(body, request.headers.authorization);
       
       reply.status(200).send(response);
     } catch (error: any) {