Set Reply-To to sellerEmail, make From display name dynamic, fix stale footer docs

Customer replies to order-confirmation and resend-verification mail now
route to the seller's real address via Reply-To, and the From display
name reflects sellerName — but the From address itself stays
admin@mk360.de since sellerEmail's domain isn't confirmed SPF-authorized
on the Hostinger account yet (see the "SMTP From address pending SPF"
memory note for the follow-up). Also cleans up README references left
over from the previous footer rewrite (stale "company line" wording, a
dangling cross-reference to a renamed section).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/lib/alertAdmin.ts

@@ -40,7 +40,11 @@ export async function sendVerificationEmail(to: string, firstName: string, token
   const url = `https://einfach-produktiv.mk360.de/api/account/verify-email?token=${token}`;
   const seller = await getSellerForInvoice();
   await transport.sendMail({
-    from: '"einfach produktiv" <admin@mk360.de>',
+    // See orderEmail.ts's own comment on why only the display name is
+    // dynamic — the address stays admin@mk360.de until sellerEmail's domain
+    // is confirmed SPF-authorized on the Hostinger account.
+    from: `"${seller?.sellerName ?? "einfach produktiv"}" <admin@mk360.de>`,
+    replyTo: seller?.sellerEmail || undefined,
     to,
     subject: "Bitte bestätige deine E-Mail-Adresse",
     html: renderVerificationEmailHtml(firstName, url, seller),

app/lib/orderEmail.ts

@@ -92,7 +92,13 @@ export async function sendOrderConfirmationEmail(order: OrderConfirmationEmailDa
   }
 
   await transport.sendMail({
-    from: '"einfach produktiv" <admin@mk360.de>',
+    // Display name only, not the address — see the memory note on why the
+    // envelope stays admin@mk360.de (that's the domain the Hostinger SMTP
+    // account is actually authorized for; sellerEmail's domain isn't
+    // confirmed SPF-authorized on it yet). Reply-To is what actually routes
+    // a customer's reply to the seller, regardless of the From address.
+    from: `"${seller?.sellerName ?? "einfach produktiv"}" <admin@mk360.de>`,
+    replyTo: seller?.sellerEmail || undefined,
     to: customerEmail,
     subject: template.subject,
     html,