add signing-key generator

scripts/keygen.py

@@ -0,0 +1,5 @@
+#!/usr/bin/env python3
+# Generate a fresh HMAC key for signing telemetry packets.
+# Prints the key once; store it in the collector's .env yourself.
+import os, base64
+print(base64.b64encode(os.urandom(32)).decode())