fix: pass VALIDATOR_SECRET_KEY to challenge containers

Orchestrator now passes VALIDATOR_SECRET_KEY env var to challenge containers
so they can sign requests for the validator worker.

Author: echobt

crates/challenge-orchestrator/src/docker.rs

@@ -550,6 +550,10 @@ impl DockerClient {
         if let Ok(validator_hotkey) = std::env::var("VALIDATOR_HOTKEY") {
             env.push(format!("VALIDATOR_HOTKEY={}", validator_hotkey));
         }
+        // Pass validator secret key for signing requests (needed by challenge validator workers)
+        if let Ok(validator_secret) = std::env::var("VALIDATOR_SECRET_KEY") {
+            env.push(format!("VALIDATOR_SECRET={}", validator_secret));
+        }
         // Pass owner/sudo hotkey for challenge sudo operations
         if let Ok(owner_hotkey) = std::env::var("OWNER_HOTKEY") {
             env.push(format!("OWNER_HOTKEY={}", owner_hotkey));