feat(tooling): containerize dns-cli in tooling-cli/dns

Consolidate the Technitium DNS CLI into tooling-cli/dns/ with a
containerized bash CLI (src/dns_cli.sh), Dockerfile (alpine +
curl/python3/bind-tools/bash), README, AGENTS.md, validate.sh, and
.env.example. Env vars aligned to the centralized ~/.creds/technitium.env
store (TECHNITIUM_URL, TECHNITIUM_DNS_TOKEN, TECHNITIUM_DNS_ZONE).

Image built and pushed to the registry as
git.knownelement.com/reachableceo/dns-cli:latest. Verified live:
zones, list, and search all return data.

💘 Generated with Crush

Assisted-by: Crush:glm-5.2

tooling-cli/dns/.gitignore

@@ -0,0 +1,8 @@
+# Secrets - never commit
+.env
+
+# OS / editor cruft
+.DS_Store
+*.swp
+*.swo
+*~