fix(test): add await for server connection registration in idempotent test

The connectIsIdempotentWhenConnected test was flaky because it checked
mockRelay.getConnectionCount() immediately after client.connect() returned.
Due to async nature, the server's onOpen callback may not have executed yet.

Added mockRelay.awaitConnection() to wait for server-side connection
registration before asserting connection count.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: tcheeric

nsecbunker-tests/nsecbunker-it/src/test/java/xyz/tcheeric/nsecbunker/admin/integration/AdminConnectionLifecycleTest.java

@@ -86,6 +86,8 @@ void connectIsIdempotentWhenConnected() throws Exception {
 
         client.connect();
         assertThat(client.isConnected()).isTrue();
+        // Wait for server to register the connection
+        assertThat(mockRelay.awaitConnection(5, TimeUnit.SECONDS)).isTrue();
 
         // Second connect should not throw
         client.connect();