feat(version-picker): update version picker to use correct property

[nineteen88]

Proposed behaviour

• update version picker to use the correct property
• reinstate the environment variable check
• add full test coverage for the version picker

Current behaviour

• version picker is currently using a property that does not exist
• no tests exist currently for version picker

Checklist

• Commits follow our style guide
• Related issues linked in commit messages if required
• Screenshots are included in the PR if useful
• All themes are supported if required
• Unit tests added or updated if required
• Playwright automation tests added or updated if required
• Storybook added or updated if required
• Translations added or updated (including creating or amending translation keys table in storybook) if required
• Typescript d.ts file added or updated if required
• Related docs have been updated if required

QA

• Tested in provided StackBlitz sandbox/Storybook
• Add new Playwright test coverage if required
• Carbon implementation matches Design System/designs
• UI Tests GitHub check reviewed if required

Additional context

Testing instructions

[Copilot]

Pull request overview

This PR fixes a critical bug in the version picker component where it was attempting to set a non-existent content property instead of the correct title property. The changes restore the environment variable check to conditionally enable the version picker and add comprehensive test coverage.

Changes:

• Fixed property reference from content to title in the version picker's item formatting logic
• Reinstated environment variable check (USE_VERSION_PICKER) to conditionally register the version picker addon
• Added comprehensive test suite covering success states, error handling, URL parameters, and fallback scenarios

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
.storybook/version-picker/index.tsx	Corrected the property name from content to title when appending "(latest)" label and updated TypeScript types
.storybook/manager.ts	Added environment variable check to conditionally register the version picker addon
.storybook/version-picker/version-picker.test.tsx	Added comprehensive test coverage including success states, error handling, HTTP failures, and URL parameter parsing

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[edleeks87]

non-blocking

Suggested change

	formattedVersions[0].title = `${formattedVersions[0].title} (latest)`;
	formattedVersions[0].title += " (latest)";