chore: modernize from .NET 7 to .NET 9

[devin-ai-integration]

Summary

Upgrades the whole solution from net7.0 to net9.0 and bumps all NuGet packages, the Dockerfile base images, and the CI workflow to matching .NET 9 releases. No source code changes were needed — build is clean and all 20 tests pass, so there were no EF Core 7→9 or ASP.NET Core breaking changes to work around.

Target framework

All six project files: net7.0 → net9.0.

Package bumps

• src/Infrastructure: EF Core (Core, Design, SqlServer, Tools) 7.0.10 → 9.0.17; Npgsql 7.0.4 → 9.0.5; Npgsql.EntityFrameworkCore.PostgreSQL + .NodaTime 7.0.4 → 9.0.4.
• src/WebApi: AspNetCore.HealthChecks.NpgSql 7.0.0 → 9.0.0; Microsoft.AspNetCore.OpenApi 7.0.9 → 9.0.17; Microsoft.EntityFrameworkCore.Design 7.0.10 → 9.0.17; Swashbuckle.AspNetCore 6.5.0 → 9.0.6.
• src/Application: Mapster 7.3.0 → 10.0.9 (only .Adapt<T>() is used, which is unchanged across majors).
• Both test projects: Microsoft.NET.Test.Sdk 17.5.0 → 18.7.0; xunit 2.4.2 → 2.9.3; xunit.runner.visualstudio 2.4.5 → 3.1.5; coverlet.collector 3.2.0 → 10.0.1; FakeItEasy 7.4.0 → 9.0.1.

Dockerfile

aspnet:7.0 / sdk:7.0 → aspnet:9.0 / sdk:9.0.

CI (.github/workflows/dotnet.yml)

dotnet-version: 6.0.x → 9.0.x; actions/checkout@v3 → @v4; actions/setup-dotnet@v3 → @v4.

docker-compose.yml

Reviewed — no .NET-version-specific references (postgres/pgadmin images are unpinned, webapi builds from the Dockerfile), so no changes.

Verification

dotnet restore / dotnet build / dotnet test all succeed locally (20/20 tests pass). Build emits only pre-existing nullable warnings, unrelated to this upgrade.

Note: the security/snyk and license/snyk CI checks are expected to fail on any dependency-changing PR in this org (org-level Snyk policy, not a code issue).

Link to Devin session: https://app.devin.ai/sessions/845c09ec5bc94c35861ebdaab8fc3435
Requested by: @joao-cognition

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