Add bundle minification practices to copilot instructions (#7963)

- Add bundle minification practices to copilot instructions

Author: konstantin-msft

.github/copilot-instructions.md

@@ -12,6 +12,30 @@ This repository contains JavaScript/TypeScript SDKs for integrating with Microso
 - Update apiExtractor reports by running `npm run apiExtractor -- --local` from the directory of each changed package.
 - Create changefiles by running `npm run beachball:change` from the root of the repo. Include PR number in changelog message.
 
+### Bundle minification practices
+
+To facilitate bundle size minification and tree-shaking, follow these practices when writing code:
+
+-   Prefer simple constants over nested ones  
+    <details>
+    <summary>Example</summary>
+
+    ```ts
+    // Prefer this (simple constant):
+    const STATUS_SUCCESS = "success";
+
+    // Over this (nested constant):
+    const STATUS = {
+        SUCCESS: "success",
+        ERROR: "error"
+    };
+    ```
+    </details>
+-   Prefer `const` objects with `as const` or literal types over TypeScript enums
+-   Prefer standalone functions over classes when possible. If using classes, keep attribute and method names short
+-   Use `const` for immutable data
+-   Avoid complex type computations (e.g., deeply nested conditional types, recursive mapped types, or types that require multiple layers of inference). Prefer simple, readable type definitions. When possible, use interfaces or type aliases with straightforward structures, and avoid advanced TypeScript features unless absolutely necessary.
+
 ## Repository Structure
 
 - `lib/`: Contains the source code for the MSAL SDKs