[CI] Rename basic CI stage-a/b/c -> base-a/b/c for symmetry with extra CI (#25420)

test/registered/observability/test_metrics.py

@@ -20,7 +20,7 @@ from sglang.test.test_utils import (
     popen_launch_server,
 )
 
-register_cuda_ci(est_time=74, stage="stage-b", runner_config="1-gpu-small")
+register_cuda_ci(est_time=74, stage="base-b", runner_config="1-gpu-small")
 register_amd_ci(est_time=32, suite="stage-b-test-1-gpu-small-amd")
 
 _MODEL_NAME = "Qwen/Qwen3-0.6B"

test/registered/observability/test_priority_metrics.py

@@ -18,7 +18,7 @@ from sglang.test.test_utils import (
 
 register_cuda_ci(
     est_time=60,
-    stage="stage-b",
+    stage="base-b",
     runner_config="1-gpu-small",
 )
 register_amd_ci(est_time=60, suite="stage-b-test-1-gpu-small-amd")

test/registered/observability/test_tracing_disaggregation.py

@@ -33,7 +33,7 @@ from sglang.utils import wait_for_http_ready
 logger = logging.getLogger(__name__)
 
 # CI registration - PD disaggregation requires 2 GPUs
-register_cuda_ci(est_time=65, stage="stage-b", runner_config="2-gpu-large")
+register_cuda_ci(est_time=65, stage="base-b", runner_config="2-gpu-large")
 
 
 class TestTraceDisaggregation(CustomTestCase):