Set sglang base image to DaoCloud mirror for China Users.

docker/china/Dockerfile

@@ -1,5 +1,10 @@
+# Use DaoCloud mirrored sglang image for China region
+FROM docker.m.daocloud.io/lmsysorg/sglang:v0.4.9.post6-cu126
+# For blackwell GPU, use the following line instead:
+# FROM docker.m.daocloud.io/lmsysorg/sglang:v0.4.9.post6-cu128-b200
+
 # Use the official sglang image
-FROM lmsysorg/sglang:v0.4.9.post6-cu126
+# FROM lmsysorg/sglang:v0.4.9.post6-cu126
 # For blackwell GPU, use the following line instead:
 # FROM lmsysorg/sglang:v0.4.9.post6-cu128-b200