Fix P1 Rust clippy: unused variable _auth_ctx, _jwt_secret, derive Default for RouterBrain

products/01-llm-cost-router/src/router/mod.rs

@@ -19,6 +19,7 @@ pub enum Complexity {
 }
 
 /// The Router Brain — evaluates request complexity and applies routing rules
+#[derive(Default)]
 pub struct RouterBrain {
     // In V1, rules are loaded from config. Later: from DB per org.
 }