fix compilation error from sed rename in idle.rs

The bulk kent→user rename turned a format string variable
reference into an undefined variable. Fixed.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

thalamus/src/idle.rs

@@ -253,7 +253,7 @@ impl State {
             self.claude_pane = Some(pane.to_string());
         }
         self.save();
-        info!("user (pane={}, {user}={from_user}) ewma={:.3}",
+        info!("user (pane={}, from_user={from_user}) ewma={:.3}",
             if pane.is_empty() { "unchanged" } else { pane },
             self.activity_ewma);
     }