feat: add Platform database model that defines the admin roles for each platform AAI-388

[marius-mather]

Description

AAI-388: add a Platform model to the database. Add an endpoint to check which platforms the current user is an admin for (to be used by the frontend in guiding which views admins see).

Changes

• Add Platform model to the database
• Make PlatformMembership refer to Platform
• Migrations for DB changes (including automatically creating the intial platforms)
• /me/platforms/admin-roles endpoint that returns which platforms the admin is a user of.
• /admin/users updated to only return users who are members of the admin's platforms
• Unit tests added and updated

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)

How to Test Manually (if necessary)

Run uv run pytest

[Copilot]

Pull Request Overview

This PR adds a Platform model to the database to define admin roles for each platform, enabling platform-specific admin access control. It updates the existing PlatformMembership model to reference the new Platform model and adds endpoints for admins to view which platforms they can manage.

• Add Platform model with admin role associations
• Update PlatformMembership to use foreign key relationship to Platform
• Add endpoint for users to check their admin platforms

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
db/models.py	Adds Platform model with admin roles relationship and updates PlatformMembership to reference Platform
routers/user.py	Adds endpoint to get platforms where current user has admin privileges
routers/admin.py	Updates user listing to filter by admin's platform access
migrations/	Database migrations to create Platform table and update constraints
tests/	Updates test files to use new Platform model and factory patterns
db/admin.py	Adds Platform model to admin interface

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[amandazhuyilan]

Looks great :) just one more thing

[amandazhuyilan]

Thanks for making the change!