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>

Makefile

@@ -0,0 +1,25 @@
+.PHONY: build run spike test tidy migrate fmt vet
+
+build:
+	go build -o bin/openmail ./cmd/openmail
+
+run: build
+	./bin/openmail serve
+
+spike:
+	go run ./spike/mimecheck
+
+migrate: build
+	./bin/openmail migrate
+
+test:
+	go test ./...
+
+tidy:
+	go mod tidy
+
+fmt:
+	go fmt ./...
+
+vet:
+	go vet ./...