docs: add private registry setup guide with env var override

- Create .env.example with placeholder URLs showing how to configure
  a private npm registry via YARN_NPM_REGISTRY_SERVER env var
- Add 'Private Registry' section to CONTRIBUTING.md explaining the
  mechanism without exposing any real corporate URLs
- No .yarnrc.yml modification needed — env vars take precedence

Author: hectoruch

.env.example

@@ -0,0 +1,21 @@
+# ============================================================
+# Yarn Berry — Registry Override (optional)
+# ============================================================
+# By default, this repo uses the public npm registry (registry.npmjs.org).
+# If your organization uses a private registry (e.g. JFrog Artifactory,
+# Nexus, GitHub Packages, etc.), set these environment variables.
+#
+# How to use:
+#   1. Copy these lines to your ~/.zshrc (or ~/.bashrc)
+#   2. Replace the placeholder URL with your organization's registry
+#   3. Run: source ~/.zshrc
+#   4. Run: yarn install
+#
+# This override applies globally to ALL Yarn Berry projects.
+# No need to modify .yarnrc.yml — the env vars take precedence.
+# ============================================================
+
+# Uncomment and configure with your private registry URL:
+# export YARN_NPM_REGISTRY_SERVER="https://your-org.example.com/artifactory/api/npm/npm-public/"
+# export YARN_NPM_ALWAYS_AUTH=true
+# export YARN_ENABLE_STRICT_SSL=false

CONTRIBUTING.md

@@ -446,6 +446,33 @@ node --version  # Should show v22.x.x
 yarn --version  # Should show 4.x.x
 ```
 
+### Private Registry (optional)
+
+This repo uses the public npm registry by default. If your organization requires a **private registry** (JFrog Artifactory, Nexus, GitHub Packages, etc.), you can override it globally via environment variables — no need to modify any files.
+
+1. Add to your `~/.zshrc` (or `~/.bashrc`):
+
+```sh
+export YARN_NPM_REGISTRY_SERVER="https://your-org.example.com/your-npm-registry/"
+export YARN_NPM_ALWAYS_AUTH=true
+export YARN_ENABLE_STRICT_SSL=false
+```
+
+2. Reload your shell:
+
+```sh
+source ~/.zshrc
+```
+
+3. Verify:
+
+```sh
+yarn config get npmRegistryServer
+# Should show your private registry URL
+```
+
+This applies globally to all Yarn Berry projects. See `.env.example` for reference.
+
 ---
 
 ## Important Notes for Contributors