Enhance error handling for composer update in env:start

[Adi-ty]

This PR improves the developer experience for npm run env:start by providing clear, actionable error messages if composer update fails.

Trac ticket: https://core.trac.wordpress.org/ticket/62807

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Props iamadisingh, azaozz.

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[azaozz]

Seems there's a left-over orphan Docker container when the Composer update fails. Maybe it can be removed at the end there?

[Adi-ty]

Seems there's a left-over orphan Docker container when the Composer update fails. Maybe it can be removed at the end there?

Thank you for the feedback! I've updated the PR to address both concerns

[azaozz]

Looks good imho.