Rebrand to INBUXA: product name, protocol greetings, sign-in page, calendar templates, logos, README

One branding module (types::brand!) supplies the name to every protocol
greeting, the HTTP realm, the startup banner, Received headers, the
user agent, the IMAP ID response and calendar PRODIDs. The sign-in and
calendar pages take ihasmail's palette and font and the INBUXA logo, and
calendar emails embed the INBUXA lockup. Default calendar and address book
names follow. Protocol identifiers (urn:stalwart:jmap, vnd.stalwart Sieve
extensions) and upstream copyright notices are unchanged.

crates/smtp/src/inbound/spawn.rs

@@ -130,7 +130,7 @@ impl<T: SessionStream> Session<T> {
             .await
             .filter(|g| !g.is_empty())
             .map(|g| format!("220 {}\r\n", g))
-            .unwrap_or_else(|| "220 Stalwart ESMTP at your service.\r\n".to_string());
+            .unwrap_or_else(|| concat!("220 ", types::brand!(), " ESMTP at your service.\r\n").to_string());
 
         if self.write(greeting.as_bytes()).await.is_err() {
             return false;