Document agent convention: commit and push to Forgejo after changes

Keeps the stack repo on the home Forgejo instance in sync when the
coding agent edits the project.

AGENTS.md

@@ -0,0 +1,8 @@
+# Agent notes (arr-stack)
+
+## Git
+
+- Remote: `origin` → `ssh://git@192.168.8.123:2222/tim/stack.git` (Forgejo `tim/stack`)
+- After any meaningful change set: **commit and push** to `main` with a clear, complete-sentence message (what changed and why).
+- Never commit secrets: `.env`, `wireguard/wg0.conf`, `config/`, GGUF models, `ansible/.secrets/`.
+- Prefer SSH push (`GIT_SSH_COMMAND` with `~/.ssh/id_ed25519` if needed).