[FIX] read value description from user dictionary correctly

[surchs]

• Closes Descriptions for discrete values are not shown in the annotation workflow #616

A couple of things I noticed while working on this:

1. If we mock store data incorrectly, i.e. not how it actually looks at runtime, then the tests pass but the app is still broken
2. It's really not very easy to get a quick sense of where information is kept in the store or what it would look like at runtime. The dev tools help, but it's still tricky to understand how a value ended up looking the way it does
3. Our e2e should help catch this but they are really hard to edit / change, so it's often easier to test manually - that's not good

Changes proposed in this pull request:

• fix store getter for value descriptions
• fix mocked data in unit test for getter

Checklist

• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see https://neurobagel.org/contributing/pull_requests for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

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[rmanaem]

🧑‍🍳