fix: missing create env functions

[brunozoric]

Summary

• Add createProcessEnv() factory to @webiny/stdlib/node — returns Env.Interface backed by process.env by default, or a custom variables record when provided
• Add createBrowserEnv() factory to @webiny/stdlib/browser — returns Env.Interface backed by a required variables record
• Both allow using Env outside of DI

Usage

Node

import { createProcessEnv } from "@webiny/stdlib/node";

// Default: reads from process.env
const env = createProcessEnv();

// Custom: pre-process variables before injection
const env = createProcessEnv({
  variables: { ...process.env, MY_VAR: "overridden" }
});

Browser

import { createBrowserEnv } from "@webiny/stdlib/browser";

const env = createBrowserEnv({
  variables: { API_URL: "https://api.example.com" }
});

Breaking changes

- BrowserEnvFeature.register() now requires { variables } param (was optional)
- ProcessEnvFeature.register() accepts optional { variables } param to override process.env