Tabs separate cases for volunteers

[maggie-larkin]

Context

• Through user research, @taysvea has found that it's rare for a volunteer to have more than one case
• So we'll want to show only one case at a time

How it works now

Volunteers assigned to multiple casa_cases see case_contact page cards stacked on top of each other.

Screenshot of Current Behavior

How it should work instead

Case Contact view per casa_case should be accessed by tabs.

Screenshot of New Behavior

Acceptance Criteria

As a volunteer
I want to only see one case
So that I can focus on one youth at a time

GIVEN I am assigned more than one case
THEN I see one case (let's do the numerically lower) as the default tab under Case Contacts
AND I see the other case as an unselected tabbed option

[Zrrrpy]

deferred due to new redesign