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/serving/integrations/llamaindex.md

@@ -0,0 +1,24 @@
+# LlamaIndex
+
+vLLM is also available via [LlamaIndex](https://github.com/run-llama/llama_index) .
+
+To install LlamaIndex, run
+
+```bash
+pip install llama-index-llms-vllm -q
+```
+
+To run inference on a single or multiple GPUs, use `Vllm` class from `llamaindex`.
+
+```python
+from llama_index.llms.vllm import Vllm
+
+llm = Vllm(
+    model="microsoft/Orca-2-7b",
+    tensor_parallel_size=4,
+    max_new_tokens=100,
+    vllm_kwargs={"gpu_memory_utilization": 0.5},
+)
+```
+
+Please refer to this [Tutorial](https://docs.llamaindex.ai/en/latest/examples/llm/vllm/) for more details.