Milestone 1 scaffold: binary skeleton, schema, deploy, Mox spike

- Confirmed core bet via spike/mimecheck: mox/message parses a messy multipart
  message standalone (envelope, MIME tree, attachment, body) with only an
  io.ReaderAt — no mox store/config. Option B is viable.
- cmd/openmail single binary: serve|migrate|smtpd|sender|version subcommands.
- internal/api: chi router, constant-time bearer auth, /healthz, stubbed v0
  AgentMail-shaped routes (501 until core services land).
- internal/store: pgxpool + embedded, idempotent, tracked SQL migrations.
- internal/store/migrations/0001_init.sql: full native schema (pods, inboxes,
  threads, messages, attachments, drafts, api_keys, webhooks, outbox, events,
  domains) with FTS + GIN indexes. Validated end-to-end against Postgres 16.
- deploy/: docker-compose (postgres+minio+openmail+caddy), Caddyfile, DNS.md
  (MX/SPF/DKIM/DMARC/DANE/MTA-STS). Makefile, .gitignore.
- Verified: go vet clean; build OK; health/auth smoke tests; migrate idempotent.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/store/store.go

@@ -0,0 +1,100 @@
+// Package store owns OpenMail's Postgres-backed persistence. This is the
+// deliberate divergence from Mox: OpenMail keeps its own native, agent-shaped
+// data model (see ARCHITECTURE.md §3) rather than embedding Mox's bstore/bbolt
+// account store.
+package store
+
+import (
+	"context"
+	"embed"
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+//go:embed migrations/*.sql
+var migrationsFS embed.FS
+
+type Store struct {
+	Pool *pgxpool.Pool
+}
+
+// Open connects to Postgres and verifies the connection.
+func Open(ctx context.Context, databaseURL string) (*Store, error) {
+	if databaseURL == "" {
+		return nil, fmt.Errorf("store: DATABASE_URL is empty")
+	}
+	pool, err := pgxpool.New(ctx, databaseURL)
+	if err != nil {
+		return nil, fmt.Errorf("store: connect: %w", err)
+	}
+	if err := pool.Ping(ctx); err != nil {
+		pool.Close()
+		return nil, fmt.Errorf("store: ping: %w", err)
+	}
+	return &Store{Pool: pool}, nil
+}
+
+func (s *Store) Close() {
+	if s.Pool != nil {
+		s.Pool.Close()
+	}
+}
+
+// Migrate applies any embedded migrations not yet recorded in schema_migrations,
+// in filename order. Each migration runs in its own transaction.
+func (s *Store) Migrate(ctx context.Context) error {
+	_, err := s.Pool.Exec(ctx, `CREATE TABLE IF NOT EXISTS schema_migrations (
+		version text PRIMARY KEY,
+		applied_at timestamptz NOT NULL DEFAULT now()
+	)`)
+	if err != nil {
+		return fmt.Errorf("migrate: ensure schema_migrations: %w", err)
+	}
+
+	entries, err := migrationsFS.ReadDir("migrations")
+	if err != nil {
+		return fmt.Errorf("migrate: read embedded migrations: %w", err)
+	}
+	names := make([]string, 0, len(entries))
+	for _, e := range entries {
+		if strings.HasSuffix(e.Name(), ".sql") {
+			names = append(names, e.Name())
+		}
+	}
+	sort.Strings(names)
+
+	for _, name := range names {
+		var exists bool
+		if err := s.Pool.QueryRow(ctx,
+			`SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE version=$1)`, name,
+		).Scan(&exists); err != nil {
+			return fmt.Errorf("migrate: check %s: %w", name, err)
+		}
+		if exists {
+			continue
+		}
+		sqlBytes, err := migrationsFS.ReadFile("migrations/" + name)
+		if err != nil {
+			return fmt.Errorf("migrate: read %s: %w", name, err)
+		}
+		tx, err := s.Pool.Begin(ctx)
+		if err != nil {
+			return fmt.Errorf("migrate: begin %s: %w", name, err)
+		}
+		if _, err := tx.Exec(ctx, string(sqlBytes)); err != nil {
+			_ = tx.Rollback(ctx)
+			return fmt.Errorf("migrate: apply %s: %w", name, err)
+		}
+		if _, err := tx.Exec(ctx, `INSERT INTO schema_migrations(version) VALUES($1)`, name); err != nil {
+			_ = tx.Rollback(ctx)
+			return fmt.Errorf("migrate: record %s: %w", name, err)
+		}
+		if err := tx.Commit(ctx); err != nil {
+			return fmt.Errorf("migrate: commit %s: %w", name, err)
+		}
+	}
+	return nil
+}