ci(warden): Use Luna 6 for auxiliary tasks (#217)

Switch the shared auxiliary model after a paired smoke comparison matched
Luna 5.6 on dedup decisions and auxiliary tool use at lower reported cost.
Preserve high reasoning effort.

Co-authored-by: GPT-6 Astra <noreply@anthropic.com>

Author: gricha

warden.toml

@@ -36,7 +36,7 @@ ignorePaths = [
 effort = "high"
 
 [defaults.auxiliary]
-model = "openrouter/openai/gpt-5.6-luna"
+model = "openrouter/openai/gpt-6-luna"
 effort = "high"
 
 [[skills]]