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/docs/deployment/docker.md

@@ -0,0 +1,13 @@
+---
+toc_depth: 2
+---
+
+# Using Docker
+
+## Pre-built images
+
+--8<-- "docs/getting_started/installation/gpu.md:pre-built-images"
+
+## Build image from source
+
+--8<-- "docs/getting_started/installation/gpu.md:build-image-from-source"