release: 0.1.0: Phases 0-11: panel, Postfix/DKIM, milter, backup, Docker image

Initial feature-complete implementation of the v1.0 specification (phases 0-11 of `docs/implementation-plan.md`).
Added:
  - Panel (Go, single static binary) with SQLite persistence, one-time
  - Domain management with per-domain DKIM (RSA-2048, generated in pure Go) and
  - Application (sender identity) management: SASL credentials via `sasldb2`,
  - Full Postfix relay config generated from env at container start: SMTPS 465,
  - Journal milter (pure Go, `go-milter`) recording every send to `send_log`;
  … (6 more in CHANGELOG)

Full detail: CHANGELOG.md (0.1.0).

internal/app/password.go

@@ -0,0 +1,27 @@
+package app
+
+import (
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+)
+
+// passwordBytes is the number of random bytes behind a generated application
+// password. 24 bytes = 192 bits of entropy, well above any brute-force concern
+// for a SASL credential the panel shows exactly once (spec 7.6.1).
+const passwordBytes = 24
+
+// generatePassword returns a strong, URL-safe random password for an
+// application's SASL account. The panel generates it, shows it once and never
+// stores the plaintext (spec 7.6.1); sasldb2 keeps only the hashed form.
+//
+// base64url output keeps the password to a safe ASCII alphabet with no shell or
+// SMTP-special characters, so it survives being typed into client configuration
+// and passed to saslpasswd2 over stdin unchanged.
+func generatePassword() (string, error) {
+	buf := make([]byte, passwordBytes)
+	if _, err := rand.Read(buf); err != nil {
+		return "", fmt.Errorf("generate password: %w", err)
+	}
+	return base64.RawURLEncoding.EncodeToString(buf), nil
+}