fix(server): use createTestLogger in unit tests

Add createTestLogger utility to provide silent pino loggers for tests.
Update test files that construct AgentRegistry, AgentManager, and
agent clients to pass the required logger parameter.

packages/server/src/test-utils/test-logger.ts

@@ -0,0 +1,5 @@
+import pino from "pino";
+
+export function createTestLogger(): pino.Logger {
+  return pino({ level: "silent" });
+}