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/http/src/api/mod.rs

@@ -267,10 +267,10 @@ pub fn accept_language(req: &HttpRequest) -> &str {
 }
 
 const BEARER_CHALLENGE: &str = concat!(
-    "Bearer realm=\"Stalwart Server\", ",
+    concat!("Bearer realm=\"", types::brand_server!(), "\", "),
     "resource_metadata=\"/.well-known/oauth-protected-resource\""
 );
-const BASIC_CHALLENGE: &str = "Basic realm=\"Stalwart Server\"";
+const BASIC_CHALLENGE: &str = concat!("Basic realm=\"", types::brand_server!(), "\"");
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum AuthChallenge {