docs: modernize contributing for agents

Author: mwfarb

CONTRIBUTING.md

@@ -1,3 +1,11 @@
-# Contribution Guide
+# Contributing to ARENA Account
 
-The Contribution Guide for all ARENA projects can be found [here](https://arena.conix.io/content/contributing.html).
+The general Contribution Guide for all ARENA projects can be found [here](https://docs.arenaxr.org/content/contributing.html).
+
+This document covers **development rules and conventions** specific to this repository. These rules are mandatory for all contributors, including automated/agentic coding tools.
+
+## Development Rules
+
+### 1. Dependencies — Pin All Versions
+
+**All dependencies must use exact, pegged versions** (no `^`, `~`, or `*` ranges). This prevents version drift across environments and ensures reproducible builds for security.