Add agent notes, coding standards, and the issue tracker

AGENTS.md

@@ -0,0 +1,16 @@
+# Agent notes
+
+This repository holds one Ansible playbook per service. Read
+[CODING_STANDARDS.md](CODING_STANDARDS.md) before adding or changing a playbook.
+
+- Layout and naming: [CODING_STANDARDS.md](CODING_STANDARDS.md).
+- Checks: run `./scripts/check.sh`. It runs yamllint, ansible-lint, and a syntax
+  check on every `*/playbook.yml`. CI runs the same script.
+- Review baseline: `origin/main`. The review diff is `git diff origin/main...HEAD`.
+- Migration spec: [docs/podman-migration.md](docs/podman-migration.md). Section 8
+  lists the repo changes the migration expects.
+- Issue tracker: [docs/agents/issue-tracker.md](docs/agents/issue-tracker.md).
+- Scratch files: write them under `.scratch/`. It is git-ignored, and `/tmp` is
+  wiped between tool calls in this environment.
+- Secrets: `vars/default.yml` holds deploy values, including passwords. Do not
+  copy a production value into a file you push to a public remote.