#1: implement F0 foundation - monorepo, migrations, Go domain layer, service skeletons, CI

Stands up the LambdaMail monorepo per PLAN.md's F0 milestone: local dev
scaffolding (.env.example, Makefile, .gitignore excluding PLAN.md/docs/
.superpowers/), the full initial Postgres schema as a golang-migrate
migration, the complete Go domain layer for services/protocols (value
objects, entities, domain events - zero external imports beyond
github.com/google/uuid) with unit tests, health-checked service skeletons
for auth/storage (TypeScript) and webmail (Next.js), a local
docker-compose.yaml wiring all services together, a language-enforcement
lint script, and a GitHub Actions CI workflow.

Built via 11 sequential tasks under subagent-driven development, each with
an independent implementer + reviewer cycle. Fixes applied during review:
DomainName.IsPunycode() added to satisfy the promised interface; ioredis
default-import typing under NodeNext; next.js bumped 15.0.3->15.5.21 to
resolve high/critical CVEs; lang-lint.mjs corrected to not flag its own
banned-terms list; web service healthcheck added so compose --wait
actually waits on it; webmail Dockerfile's missing public/ directory:
protocols go.mod version aligned with CI's Go 1.22 pin.

Known follow-ups for later phases (not blocking F0): go-arch-lint isn't
wired into CI yet; live docker compose up and migration apply have not
been exercised in this dev environment (no Docker/psql available here)
and will get their first real run in CI, which does have Docker.

services/protocols/internal/domain/valueobject/delivery_status_code_test.go

@@ -0,0 +1,29 @@
+package valueobject
+
+import "testing"
+
+func TestNewDeliveryStatusCode_AcceptsSuccess(t *testing.T) {
+	c, err := NewDeliveryStatusCode(2, 0, 0)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if c.String() != "2.0.0" {
+		t.Errorf("String() = %q, want %q", c.String(), "2.0.0")
+	}
+}
+
+func TestNewDeliveryStatusCode_AcceptsPermanentFailure(t *testing.T) {
+	c, err := NewDeliveryStatusCode(5, 1, 1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if c.String() != "5.1.1" {
+		t.Errorf("String() = %q, want %q", c.String(), "5.1.1")
+	}
+}
+
+func TestNewDeliveryStatusCode_RejectsInvalidClass(t *testing.T) {
+	if _, err := NewDeliveryStatusCode(3, 0, 0); err == nil {
+		t.Fatal("expected error: RFC 3463 only defines classes 2, 4 and 5, got nil")
+	}
+}