fix: process.env.NODE_ENV error in bundling

[yhyuan]

Closes #29995

What I did

This PR assign process.env.NODE_ENV to be "production" when esbuild bundles for browser. It will avoid executing the code snippets which should not executed in production environment.

Before applying the changes, the bundling result (by running yarn build core) for @storybook/core/dist/theming/index.js contains the following code snippets.

if (true) {
  ClassNames.displayName = "EmotionClassNames";
}
if (true) {
  isBrowser3 = true;
  isTestEnv = typeof jest !== "undefined" || typeof vi !== "undefined";
  if (isBrowser3 && !isTestEnv) {
    globalContext = // $FlowIgnore
    typeof globalThis !== "undefined" ? globalThis : isBrowser3 ? window : global;
    globalKey = "__EMOTION_REACT_" + pkg.version.split(".")[0] + "__";
    if (globalContext[globalKey]) {
      console.warn("You are loading @emotion/react when it is already loaded. Running multiple instances may cause problems. This can happen\
 if multiple versions are used, or if multiple builds of the same version are used.");
    }
    globalContext[globalKey] = true;
  }
}
var isBrowser3;
var isTestEnv;
var globalContext;
var globalKey;

The four variables are defined after they have been used.

After applying the changes, the bundling result (by running yarn build core) for @storybook/core/dist/theming/index.js contains the following code snippets.

if (false) {
  ClassNames.displayName = "EmotionClassNames";
}
if (false) {
  isBrowser3 = true;
  isTestEnv = typeof jest !== "undefined" || typeof vi !== "undefined";
  if (isBrowser3 && !isTestEnv) {
    globalContext = // $FlowIgnore
    typeof globalThis !== "undefined" ? globalThis : isBrowser3 ? window : global;
    globalKey = "__EMOTION_REACT_" + pkg.version.split(".")[0] + "__";
    if (globalContext[globalKey]) {
      console.warn("You are loading @emotion/react when it is already loaded. Running multiple instances may cause problems. This can happen\
 if multiple versions are used, or if multiple builds of the same version are used.");
    }
    globalContext[globalKey] = true;
  }
}
var isBrowser3;
var isTestEnv;
var globalContext;
var globalKey;

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

Greptile Summary

Based on the provided information, I'll create a concise summary of the pull request focusing on the key changes and their impact.

Fixes bundling issue by ensuring proper NODE_ENV setting during build process to prevent development code from appearing in production builds.

• Modified esbuild configuration to set process.env.NODE_ENV to "production" for browser bundles
• Prevents execution of development-only code blocks in production environment
• Fixes variable hoisting issue in @storybook/core/dist/theming/index.js
• Resolves issue [Bug]: variables are used before they are defined. #29995 where variables were being accessed before definition
• Improves bundle output by correctly handling conditional code execution

The changes ensure development code like variable declarations and debug messages are properly excluded from production builds, leading to cleaner and more efficient bundled output.

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[greptile-apps]

LGTM

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[greptile-apps]

LGTM

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