fix: suppress spurious chat message on script skip

When a script returns wakeAgent=false, set result to null so the host
doesn't forward an internal status string to the user's chat.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

container/agent-runner/src/index.ts

@@ -566,7 +566,7 @@ async function main(): Promise<void> {
       log(`Script decided not to wake agent: ${reason}`);
       writeOutput({
         status: 'success',
-        result: `Script: ${reason}`,
+        result: null,
       });
       return;
     }