P6.2: Fix verification script shebang for NixOS compatibility

The script had #!/bin/bash which doesn't exist on NixOS systems.
Changed to #!/usr/bin/env bash for portability.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/verify_p6_2_peer_discovery.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Verification script for P6.2 Peer Discovery
 # Tests that peer discovery is properly configured and the miroir_peer_pod_count metric exists