frontend: AppContainer.stories: rename withEnv to WithEnv to fix rules-of-hooks

[jedbillyb]

Fixes #5184

Renames withEnv decorator to WithEnv (PascalCase) so React
recognises it as a component and hooks are valid per rules-of-hooks.

Steps to test:

• Run npx eslint src/components/App/AppContainer.stories.tsx - no warnings

[k8s-ci-robot]

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[Copilot]

Pull request overview

This PR addresses an ESLint react-hooks/rules-of-hooks warning in the Storybook story for AppContainer by renaming a hooks-using decorator to PascalCase so it is treated as a React component by the hooks rules.

Changes:

• Renamed the Storybook decorator withEnv to WithEnv.
• Updated the story’s decorators array to reference WithEnv.

[skoeva]

can you squash the merge commits in this PR? these docs should be helpful