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/template_teleflm.jinja

@@ -0,0 +1,12 @@
+{%- for message in messages %}
+    {%- if message['role'] == 'user' %}
+        {{- '<_user>' + message['content']|trim }}
+    {%- elif message['role'] == 'system' %}
+        {{- '<_system>' + message['content']|trim }}
+    {%- elif message['role'] == 'assistant' %}
+        {{- '<_bot>' + message['content'] }}
+    {%- endif %}
+{%- endfor %}
+{%- if add_generation_prompt %}
+    {{- '<_bot>' }}
+{%- endif %}