feat: implement strangler-fig-demo Session 1 (backend + smoke script)

Builds the four-seam, three-write-path reference demo backend: case-framework
(seam D stand-in), legacy-backend/frontend (SQL Server, seams A/B/C targets),
and new-backend (Domain/Application/Infrastructure.*/Api implementing the
source resolver, take/release-ownership, write-through translator, and owned
assessment flow), wired together via docker-compose with a plain placeholder
frontend standing in for the Angular portal until Session 2.

All 11 Architecture.Tests pass and scripts/smoke.sh passes end-to-end against
a fresh `docker compose up`, covering acceptance criteria 1-3 and 7-22.

Fixes two real domain bugs found only once the stack ran for real: the BSN
eleven-proof checksum trivially passes all-zero digits, and the adoption
mapper silently treated a partial legacy address as absent instead of failing
loudly. Also fixes several environment-specific integration issues (rootless
Podman/SELinux bind-mount permissions, a buildah NuGet layer-caching bug,
SqlClient's invariant-globalization incompatibility, and an nginx path-prefix
mismatch for the legacy frontend).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

new/src/New.Infrastructure.Persistence/NewDbContextFactory.cs

@@ -0,0 +1,21 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Design;
+
+namespace New.Infrastructure.Persistence;
+
+/// <summary>
+/// Design-time-only factory so `dotnet ef migrations add/update` can
+/// construct a NewDbContext without a running host (this project has no DI
+/// container of its own - New.Api's ServiceCollectionExtensions.AddPersistenceInfrastructure
+/// is what wires the real DbContextOptions at runtime, reading
+/// ConnectionStrings__New from the environment). Never used outside `dotnet ef`.
+/// </summary>
+public sealed class NewDbContextFactory : IDesignTimeDbContextFactory<NewDbContext>
+{
+    public NewDbContext CreateDbContext(string[] args)
+    {
+        var optionsBuilder = new DbContextOptionsBuilder<NewDbContext>();
+        optionsBuilder.UseNpgsql("Host=localhost;Port=5432;Database=newdb;Username=postgres;Password=postgres");
+        return new NewDbContext(optionsBuilder.Options);
+    }
+}