Product: Define the workflow for staff whose emails are decommissioned by the city

### Overview
We need to define what happens to the TDM Plans they are assigned to when a users permission is either downgraded or removed.

#### Details
We need to define what happens when a city staff person leaves no longer works on TDM Plans, either because they move to a different department or role, or they leave city employment and their email is decomissioned.

notes from meeting 2026-06-23
- https://github.com/hackforla/tdm-calculator/issues/3010#issuecomment-4794192962

>Q: Also, what should happen when staff members accounts are archived. 2. Does it unassign them from from the previous TDM Plans they have reviewed? Approved or unapproved?

A: Stakeholders would like to keep people assigned after they leave. HfLA suggests historical details of who was assigned if reassignment happens.

Currently the application has a bug which is affecting modals and overlays with dates. So we cannot check to see if that information is visable in the edit modal on the Manage Submissions page.

### Action Items
- [ ] [INSERT ACTIONS

- [ ] Review with product and dev. Update if needed based on feedback
- [ ] Once finalized, add before and after images to the slide in the staging deck for this issue (see link under resources)
- [ ] Get Stakeholder sign-off via the stakeholder meeting slide deck.

### Resources/Instructions

#### Staging and Release decks
- [Staging Deck](https://docs.google.com/presentation/d/1crZ3IxqA4hAu3qzD7ns93Ieuqjwh6wyEtuX_46cP-fg/)
- [Staging slide, ISSUE NUMBER]
- Release Deck
- [2025-MM-DD Release deck, slide ISSUE NUMBER]

Start with the linked meeting notes in issue 3010 and review the Manage Submissions edit modal, including the current date-related modal and overlay bug. Define the behavior for downgraded, removed, or decommissioned staff accounts, then review it with product and development, add staging and release-deck images, and obtain stakeholder sign-off.

Written by the indexing model from the issue text.