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/jmap-proto/src/request/capability.rs

@@ -407,7 +407,7 @@ impl Session {
 impl Default for SieveSessionCapabilities {
     fn default() -> Self {
         Self {
-            implementation: "Stalwart v1.0.0",
+            implementation: concat!(types::brand!(), " v1.0.0"),
         }
     }
 }