Add AGENTS.md and CLAUDE.md for coding agents

Ground rules, building and testing with real BIND, where things live,
web UI rules, BIND gotchas, and the git and release workflow.
docs/development.md lists the packages its layout was missing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/development.md

@@ -32,6 +32,12 @@ internal/
   blocking/           blocklist parser, response policy zone writers, and matching a name the way named does
                       (the downloads are in engine/blocklists.go)
   config/             jarld's YAML configuration
+  certs/              certificates: Jarl as an ACME client (lego), renewal, files for named
+  encdns/             encrypted DNS (DoT/DoH) setup, status and health checks
+  mailcheck/          reverse DNS check of the addresses mail is sent from
+  totp/               two-factor login codes and recovery codes
+  version/            what a build reports (release tag, commit, commits since a tag)
+  testutil/           test helpers, chiefly finding BIND's tools (JARL_BIND_ROOT)
 deploy/               systemd units (jarld, the daily backup service and timer), sysusers.d and tmpfiles.d files
 deploy/debian/        the Debian package's control template and postinst/prerm/postrm
 contrib/acme.sh/      acme.sh DNS API hook