Add agent rule for integration test database cleanup

[Copilot]

Without guidance, AI agents adding new entities can forget to update ResetDatabaseAsync or skip extending IntegrationTestBase, causing test pollution across the suite.

Changes

• .github/agents/integration-tests.md — new agent rule file covering:
  • Every DbSet<T> in ApplicationDbContext must have a matching RemoveRange in ResetDatabaseAsync, children before parents (FK order)
  • All test classes must extend IntegrationTestBase — this is the mechanism that calls ResetDatabaseAsync before each test
  • Entities with shared fixtures (e.g. admin user) need conditional cleanup, not unconditional RemoveRange
  • Reference table of current entities and their FK dependencies for correct deletion ordering
  • Concrete code example for adding a new entity + its cleanup

Example (from the rule)

// 1. Add DbSets to ApplicationDbContext
public DbSet<Foo> Foos => Set<Foo>();
public DbSet<FooItem> FooItems => Set<FooItem>();

// 2. Add cleanup to ResetDatabaseAsync — child before parent
db.FooItems.RemoveRange(db.FooItems);
db.Foos.RemoveRange(db.Foos);

// 3. Test class must extend IntegrationTestBase
public class FooEndpointTests(PostgresContainerFixture postgres)
    : IntegrationTestBase(postgres) { }

Original prompt

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This section details on the original issue you should resolve

<issue_title>Test agent rule</issue_title>
<issue_description>Please create an agent rule for integration tests, that ensures that database cleanup method contains all new entities, and that the method is always called.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Test agent rule #66

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