Add vLLM v0.18.1 source tree with KV transfer abort fix

third_party/vllm/ now tracked in git for direct patch management.
Based on vLLM v0.18.1 release with one patch applied:

  vllm/v1/core/sched/scheduler.py:
    Replace fatal assert with graceful skip when KV transfer callback
    arrives for an already-aborted request during PD disaggregated serving.

Future vLLM modifications should be made directly in third_party/vllm/
and committed normally. The patches/ directory is kept as documentation
of what changed from upstream.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

third_party/vllm/examples/online_serving/prometheus_grafana/prometheus.yaml

@@ -0,0 +1,10 @@
+# prometheus.yaml
+global:
+  scrape_interval: 5s
+  evaluation_interval: 30s
+
+scrape_configs:
+  - job_name: vllm
+    static_configs:
+      - targets:
+          - 'host.docker.internal:8000'