feat(litellm): default glm-5.1 to thinking-off; add glm-5.1-reasoning opt-in

glm-5.1 now disables GLM thinking by default via extra_body (LiteLLM strips
top-level thinking under drop_params but forwards extra_body verbatim to z.ai).
New glm-5.1-reasoning alias = same upstream with thinking enabled, so reasoning
is opt-in. Operator call 2026-06-11; primary driver is the pi coding harness.
Verified live: glm-5.1 reasoning_tokens=0, glm-5.1-reasoning reasoning_tokens>0.

stacks/litellm/conf/config.yaml

@@ -53,11 +53,27 @@ model_list:
   #     wildcard below (no collision with llama-swap's glm4.7-flash etc.
   #     — different model IDs). NOTE: paid API; only gateway-keyed callers
   #     can reach these, but they DO spend z.ai credits. Key in .env. ---
+  # glm-5.1: thinking DISABLED by default (2026-06-11, operator call). LiteLLM
+  #   strips a top-level `thinking` param (drop_params), but forwards `extra_body`
+  #   verbatim to z.ai, where the native thinking:{type:disabled} control lands —
+  #   verified reasoning_tokens→0. Reasoning is opt-in via glm-5.1-reasoning below.
   - model_name: glm-5.1
     litellm_params:
       model: openai/glm-5.1
       api_base: https://api.z.ai/api/coding/paas/v4
       api_key: os.environ/Z_AI_API_KEY
+      extra_body:
+        thinking:
+          type: disabled
+  # glm-5.1-reasoning: identical upstream, thinking ENABLED (opt-in reasoning).
+  - model_name: glm-5.1-reasoning
+    litellm_params:
+      model: openai/glm-5.1
+      api_base: https://api.z.ai/api/coding/paas/v4
+      api_key: os.environ/Z_AI_API_KEY
+      extra_body:
+        thinking:
+          type: enabled
   - model_name: glm-5-turbo
     litellm_params:
       model: openai/glm-5-turbo