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/email/src/message/crypto.rs

@@ -110,7 +110,7 @@ impl EncryptMessage for Message<'_> {
             outer_message.extend_from_slice(
                 concat!(
                     "\"\r\n\r\n",
-                    "OpenPGP/MIME message (Automatically encrypted by Stalwart)\r\n\r\n",
+                    concat!("OpenPGP/MIME message (Automatically encrypted by ", types::brand!(), ")\r\n\r\n"),
                     "--"
                 )
                 .as_bytes(),