Add linting section to AGENTS.md (#61)

Ensures AI assistants run `make lint` and fix all issues before
considering work done.

Author: SeanTAllen

AGENTS.md

@@ -25,3 +25,7 @@ Read [CONTRIBUTING.md](CONTRIBUTING.md).
 ## Prose model
 
 If you are running on an Anthropic model, use `claude-opus-4-6` for writing comments, documentation, and other prose. Prose quality from Anthropic models dropped starting with Opus 4.7 and has gotten worse with each subsequent release.
+
+## Linting
+
+Run `make lint` before considering any work done. Fix all issues it reports. `make lint` runs pony-lint, which checks for style and correctness problems in Pony source files. A clean lint run is part of "done" — don't open a PR or report completion with lint issues outstanding.