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>

ARCHITECTURE.md

@@ -189,11 +189,12 @@ cmd/openmail/         # single binary: `serve`, `smtpd`, `sender`, `mcp` subcomm
 internal/core/        # inbox/message/thread/draft services
 internal/smtp/        # go-smtp inbound server; calls mox verify/parse/junk + threading
 internal/sender/      # Sender interface: smtp (mox smtpclient+dane+mtasts) & relay backends; mox dkim
-internal/store/       # sqlc queries, object-store client
+internal/store/             # pgx/sqlc queries, object-store client, embedded migrations
+internal/store/migrations/  # SQL migrations (go:embed'd into the binary)
 internal/api/         # chi HTTP handlers (v0 surface)
 internal/mcp/         # MCP server over core
 deploy/               # docker-compose.yml, Caddyfile, DNS (MX/SPF/DKIM/DMARC/DANE/MTA-STS) notes
-db/migrations/        # SQL migrations
+spike/                # throwaway feasibility spikes (mimecheck: mox standalone parse — PASSED)
 ```
 
 ## 8. Licensing & attribution