Scope UserLab listing to selected lab

[AlexMeng0831]

Describe your changes

I made a follow-up fix on fix/userlab-lab-filter for the getUserLabs issue. The list endpoint now requires a labId, checks that the caller belongs to that lab, and only returns memberships for that lab instead of the whole system. I also updated the related route/service tests.

Issue ticket number and link

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Checklist before requesting a review

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• This change requires a documentation update