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.Application/Ports/ICaseFrameworkGateway.cs

@@ -0,0 +1,25 @@
+namespace New.Application.Ports;
+
+public sealed record CaseCreated(Guid CaseId, string? ProcessStatus);
+
+public sealed record TaskCreated(Guid TaskId, bool Open);
+
+/// <summary>Seam D: the case-framework client port (New.Infrastructure.CaseFramework implements this).</summary>
+public interface ICaseFrameworkGateway
+{
+    Task<CaseCreated> CreateCaseAsync(string caseTypeCode, string externalReference, IReadOnlyList<string> participants, CancellationToken ct);
+
+    Task<string?> GetProcessStatusAsync(Guid caseId, CancellationToken ct);
+
+    Task<TaskCreated> CreateTaskAsync(Guid caseId, string code, string description, CancellationToken ct);
+
+    Task CompleteTaskAsync(Guid caseId, Guid taskId, CancellationToken ct);
+
+    /// <summary>
+    /// POST .../closure-request. Returns true if the case closed, false if
+    /// the framework returned 409 (an open task) - which is an expected,
+    /// non-exceptional outcome for callers (e.g. the owned assessment flow
+    /// treats it as "closure pending", not a failure).
+    /// </summary>
+    Task<bool> RequestClosureAsync(Guid caseId, CancellationToken ct);
+}