refine: drop temperature param for Opus 4.8

Claude Opus 4.8 rejects `temperature` — 'deprecated for this model'.
Newer models manage their own sampling; the parameter is only legal
on older Claude generations. Dropping it wholesale rather than
version-gating since we default to Opus 4.8.

Verified: cargo check clean.

crates/cm-api/src/mission_refiner.rs

@@ -130,10 +130,11 @@ async fn call_anthropic(
         }
     );
 
+    // Opus 4.8 rejects the `temperature` parameter — the model runs at
+    // its own calibrated setting. Older Claude models accepted 0.0–1.0.
     let body = json!({
         "model": model,
         "max_tokens": 4096,
-        "temperature": 0.3,
         "system": system,
         "messages": [
             { "role": "user", "content": user }