add AGENTS.md (#495)

* add AGENTS.md

* explain python package usage

Author: moritz-gross

AGENTS.md

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+# Agent Notes (MathCAT)
+
+Purpose: fast orientation for coding agents. try to keep low overlap with README.md etc., 
+but add common mistakes of AI agents here instead.
+
+## Project Scope
+- MathCAT converts MathML to speech, braille, and navigation output.
+- Core flow: `set_mathml()` -> `canonicalize.rs` -> optional `infer_intent.rs` -> `speech.rs` / `braille.rs`.
+
+## Rules System (`Rules/`)
+- YAML rules are loaded at runtime by domain:
+- Common per-language files:
+  - `ClearSpeak_Rules.yaml`, `SimpleSpeak_Rules.yaml`
+  - `SharedRules/`, `unicode.yaml`, `unicode-full.yaml`, `definitions.yaml`, `navigate.yaml`
+- `build.rs` can bundle rules into `rules.zip` when `include-zip` is enabled.
+
+## Translation Conventions
+- `t:` means untranslated or unverified.
+- `T:` means translated and verified.
+- tool for comparing rules across languages: `uv run --project PythonScripts audit-translations <language-code>`
+
+## Python Tooling (`uv`)
+- `uv` is the Python dependency and project manager for repo tooling. Use `uv run <command-name>`
+- discuss new packages before adding them. use `uv add <package-name>` and `uv sync` on confirmation
+- In sandboxed runs, if needed:
+  - set `UV_CACHE_DIR=/tmp/uv-cache`
+  - rerun with escalated permissions if macOS `system-configuration` panics occur.
+- *always* self-validate: `ùv run pytest`
+
+## Agent Instructions
+- Do not mirror README content here; keep guidance agent-specific.
+- Avoid broad formatting sweeps; do not run `cargo fmt` in this repo.
+- Keep code/rule changes focused and validate with targeted tests first: `cargo test <relevant-tests>`
+- do not do any git commands unless explicitly asked for
+- Rust coverage is in `target/coverage/`.