feat(mail): one layout for all mails with logo, greeting, cards and footer

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/mail_test.go

@@ -284,3 +284,30 @@ func TestSenderAddressGetsDisplayName(t *testing.T) {
 		}
 	}
 }
+
+// HTML mails carry the logo as an inline part (multipart/related), plain mails stay single-part
+func TestMailLayoutEmbedsLogo(t *testing.T) {
+	text, htmlBody := renderMail(mailContent{
+		Greeting: "Hallo Anna",
+		Intro:    "Eine Aufgabe ist fällig <jetzt>:",
+		Sections: []mailSection{{Title: "Heute", Items: []mailItem{{Title: "Zahnarzt & Co", Meta: "15:30 Uhr"}}}},
+		Button:   &mailButton{Label: "Öffnen", URL: "https://mindsift.example/"},
+		Footer:   "Fußzeile",
+	})
+	if !strings.Contains(text, "HEUTE\n• Zahnarzt & Co (15:30 Uhr)") || !strings.Contains(text, "Öffnen: https://mindsift.example/") {
+		t.Fatalf("text version wrong:\n%s", text)
+	}
+	if !strings.Contains(htmlBody, "Zahnarzt &amp; Co") || !strings.Contains(htmlBody, "&lt;jetzt&gt;") {
+		t.Fatalf("HTML must escape content")
+	}
+	msg := string(buildMessage("MindSift <a@example.com>", "b@example.com", "Test", text, htmlBody, time.Now()))
+	for _, want := range []string{"multipart/alternative", "multipart/related", "Content-ID: <" + mailLogoCID + ">", "Content-Type: image/png"} {
+		if !strings.Contains(msg, want) {
+			t.Fatalf("message lacks %q", want)
+		}
+	}
+	plain := string(buildMessage("a@example.com", "b@example.com", "Test", "nur Text", "", time.Now()))
+	if strings.Contains(plain, "multipart") || strings.Contains(plain, "image/png") {
+		t.Fatalf("plain mail must stay single-part")
+	}
+}