#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/entity/domain.go

@@ -0,0 +1,44 @@
+// Package entity contains the domain's aggregate roots and entities (Clean Architecture layer 1).
+package entity
+
+import (
+	"errors"
+
+	"lambdamail/protocols/internal/domain/valueobject"
+)
+
+// Domain is the aggregate root for a hosted mail domain (PLAN.md section 3).
+type Domain struct {
+	name               valueobject.DomainName
+	active             bool
+	activeMailboxCount int
+}
+
+var ErrDomainHasActiveMailboxes = errors.New("domain: cannot deactivate while it has active mailboxes")
+
+func NewDomain(name valueobject.DomainName) *Domain {
+	return &Domain{name: name, active: true}
+}
+
+func (d *Domain) Name() valueobject.DomainName { return d.name }
+func (d *Domain) IsActive() bool               { return d.active }
+func (d *Domain) ActiveMailboxCount() int      { return d.activeMailboxCount }
+
+// RegisterMailboxCreated tracks a newly created active mailbox under this domain.
+func (d *Domain) RegisterMailboxCreated() { d.activeMailboxCount++ }
+
+// RegisterMailboxRemoved tracks a mailbox no longer counted as active under this domain.
+func (d *Domain) RegisterMailboxRemoved() {
+	if d.activeMailboxCount > 0 {
+		d.activeMailboxCount--
+	}
+}
+
+// Deactivate enforces the invariant "cannot deactivate with active mailboxes" (PLAN.md section 3).
+func (d *Domain) Deactivate() error {
+	if d.activeMailboxCount > 0 {
+		return ErrDomainHasActiveMailboxes
+	}
+	d.active = false
+	return nil
+}