chore: clean up dev scratch files from project root

- Remove rndc-key from tracking, add to .gitignore
- Move async_sms_send.py, demo_threshold.py, nagios_bad.sh to scripts/

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

.gitignore

@@ -13,3 +13,4 @@ ssl/
 uv.lock
 .hb.yaml
 .superpowers/
+rndc-key

rndc-key

@@ -1,4 +0,0 @@
-key "rndc-key" {
-      algorithm hmac-md5;
-      secret "qlGa+AYKtyOgWNuozqECMw==";
-};