feat(mail): deliver email one-time codes over SMTP and add the setup email screen

Felis never actually sent mail: OTP codes for onboarding, email login and
op-login were only written to the felis-api log behind a "demo has no SMTP"
limitation, and the Settings/SMTP flow those comments promised was never
built. Combined with the bootstrap Owner's address being recorded unverified
(87279a1), op-login start always took the anti-enumeration neutral branch and
minted a fake request_id, so the in-game approve inevitably answered "No
pending operator sign-in with that code".

Give the codes a real delivery path, configured in felis.toml rather than a
web settings page so config keeps a single source of truth:

- config: new [smtp] table (host, port defaulting to 587, from, username,
  password_ref). Validation requires a plausible from address and a sane
  port; the password itself never enters the config file.
- internal/mail (new): stdlib net/smtp mailer implementing the api.OTPMailer
  seam. Port 465 dials implicit TLS, other ports upgrade via STARTTLS when
  advertised; AUTH only when a username is configured (PlainAuth itself
  refuses plaintext, so the password cannot leak to a TLS-less relay).
  Ping() proves reachability and credentials without sending mail. The
  message shape (CRLF, Q-encoded bilingual subject) is pinned by test.
- platform: felis-smtp Secret constants and an optional FELIS_SMTP_PASSWORD
  env var on the felis-api Deployment, mirroring felis-uploads-s3.
- cmd/felis api: construct the real mailer when [smtp] is configured; keep
  the log fallback otherwise and say so at startup. Warn when a username is
  set but the credentials env is empty.
- setup TUI: "e" on the summary/status screen opens the email form (host,
  port, from, optional auth). Apply order: Ping preflight, [smtp] into both
  host and pod config files, felis-smtp Secret piped to kubectl via stdin,
  config Secret, felis-api rollout. A failed preflight leaves the install
  untouched. SMTP is deliberately not a wizard rail step: first-run stays
  mail-less by design, and the passkey minted at onboarding is the pre-SMTP
  owner credential.

Also make PGRepo.UserByEmail match case-insensitively (lower(email) =
lower($1)), honoring the interface contract and the users_verified_email_
unique partial index; the fake repo already matched with EqualFold.

Existing installs need the felis-api Deployment manifest re-applied (e.g. a
bootstrap re-run) before the new env var exists; a rollout restart alone
cannot add it.

internal/config/config_test.go

@@ -405,3 +405,53 @@ url = "postgres://felis@db/felis"
 		t.Fatal("expected error for unknown key")
 	}
 }
+
+// TestLoadSMTPDefaultsPort pins the [smtp] contract: a host with no port gets the
+// 587 STARTTLS default, and an absent [smtp] block stays fully zero (no mailer).
+func TestLoadSMTPDefaultsPort(t *testing.T) {
+	cfg, err := config.Load(writeTOML(t, `
+[server]
+root_domain = "mc.example.net"
+[database]
+url = "postgres://felis@db/felis"
+[smtp]
+host = "smtp.example.net"
+from = "[email protected]"
+`))
+	if err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+	if cfg.SMTP.Port != 587 {
+		t.Errorf("smtp port = %d, want the 587 default", cfg.SMTP.Port)
+	}
+
+	cfg, err = config.Load(writeTOML(t, `
+[server]
+root_domain = "mc.example.net"
+[database]
+url = "postgres://felis@db/felis"
+`))
+	if err != nil {
+		t.Fatalf("Load without [smtp]: %v", err)
+	}
+	if cfg.SMTP.Host != "" || cfg.SMTP.Port != 0 {
+		t.Errorf("absent [smtp] must stay zero, got %+v", cfg.SMTP)
+	}
+}
+
+// TestLoadRejectsSMTPWithoutFrom guards the deliverability rule: naming a relay
+// host commits the block to being sendable, so a missing/invalid From fails at
+// load rather than at the first OTP a player is waiting on.
+func TestLoadRejectsSMTPWithoutFrom(t *testing.T) {
+	_, err := config.Load(writeTOML(t, `
+[server]
+root_domain = "mc.example.net"
+[database]
+url = "postgres://felis@db/felis"
+[smtp]
+host = "smtp.example.net"
+`))
+	if err == nil {
+		t.Fatal("expected error when [smtp] host is set without a from address")
+	}
+}