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/dashboards/perses/README.md

@@ -0,0 +1,48 @@
+# Perses Dashboards for vLLM Monitoring
+
+This directory contains Perses dashboard configurations designed to monitor vLLM
+performance and metrics.
+
+## Requirements
+
+- Perses instance (standalone or via operator)
+- Prometheus data source configured in Perses
+- vLLM deployment with Prometheus metrics enabled
+
+## Dashboard Format
+
+We provide dashboards in the **native Perses YAML format** that works across all
+deployment methods:
+
+- **Files**: `*.yaml` (native Perses dashboard specifications)
+- **Format**: Pure dashboard specifications that work everywhere
+- **Usage**: Works with standalone Perses, API imports, CLI, and file provisioning
+- **Kubernetes**: Directly compatible with Perses Operator
+
+## Dashboard Descriptions
+
+- **performance_statistics.yaml**: Performance metrics with aggregated latency
+  statistics
+- **query_statistics.yaml**: Query performance and deployment metrics
+
+## Deployment Options
+
+### Direct Import to Perses
+
+Import the dashboard specifications via Perses API or CLI:
+
+```bash
+percli apply -f performance_statistics.yaml
+```
+
+### Perses Operator (Kubernetes)
+
+The native YAML format works directly with the Perses Operator:
+
+```bash
+kubectl apply -f performance_statistics.yaml -n <namespace>
+```
+
+### File Provisioning
+
+Place the YAML files in a Perses provisioning folder for automatic loading.