ci: add justfile for RSR compliance

Adds minimal justfile with default listing and panic-attack assail
target as required by the hyperpolymath RSR standard.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hyperpolymath

justfile

@@ -0,0 +1,9 @@
+# SPDX-License-Identifier: PMPL-1.0-or-later
+# Justfile for network-dashboard
+
+default:
+    @just --list
+
+# Run panic-attack assail
+assail:
+    panic-attack assail .