[#12588] Improve test code coverage of visibility message pipes

[AlanRQiu]

Part of #12588

Description
This PR improves the test coverage for the VisibilityCapabilityPipe and VisibilityEntityNamePipe.

Changes
Added unit tests to visibility-capability.pipe.spec.ts covering all logical branches.
Added unit tests to visibility-entity-name.pipe.spec.ts covering entity pluralization and default "unknown" cases.

Verification Results
All tests passed locally using npm test.

[github-actions]

Hi @AlanRQiu, thank you for your interest in contributing to TEAMMATES!
However, your PR does not appear to follow our contribution guidelines:

• Description must reference the issue number the PR is fixing, e.g. Fixes #<issue-number> (or Part of #<issue-number> if the PR does not address the issue fully)

Please address the above before we proceed to review your PR.

[samuelfangjw]

Thank you for your interest in contributing, please ensure all tests pass before we go ahead and review this PR.

[samuelfangjw]

Closing due to inactivity to keep things tidy and so others can work on it. If you’d like to continue working on it, feel free to reopen the PR or create a new one anytime. Thanks for your contribution!