fix(litellm): default max_tokens=4096 for the reasoning model

Qwen3 spends output tokens on reasoning_content before writing content.
Open WebUI's default chat request doesn't set max_tokens, so it fell
through to llama.cpp's low default and the model ran out mid-thought,
returning finish_reason=length with empty content — no reply shown in
Open WebUI. Confirmed via a manual /v1/chat/completions call: works with
max_tokens=2000, fails without it.

litellm_params.max_tokens is a default, not a cap — any caller (or Open
WebUI's per-model Advanced Params) that sets its own max_tokens still
overrides it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Q2CR8yawSf7pwAVYnjwFea

litellm-config.yaml

@@ -7,6 +7,13 @@ model_list:
       model: openai/qwen3.8-27b-local
       api_base: http://llama-server:8080/v1
       api_key: local
+      # Qwen3 is a reasoning model — it spends output tokens on
+      # reasoning_content before ever writing content. Callers that don't
+      # set their own max_tokens (Open WebUI's default request didn't) hit
+      # llama.cpp's low default, so the model runs out mid-thought and
+      # content comes back empty. This is a floor, not a cap — any caller
+      # that passes its own max_tokens still overrides it.
+      max_tokens: 4096
     model_info:
       # Shadow cloud-cost estimate — priced against Claude Sonnet 5's published
       # rate, not real spend (this proxy only ever routes to the local model).