Write the brand in lowercase where people see it

The name is inbuxa, lowercase, like the wordmark; INBUXA reads as an
acronym. The admin and webmail already changed. Here that's everything
the server shows people: the brand macro behind the protocol greetings,
the HTTP and SCIM realms, the startup banner and the calendar and contact
PRODID; the first-party OAuth client descriptions; the legacy-protocol
refusals; the default calendar and address book names and the SMTP
greeting default, in the code and the schema served to the admin
(checksum regenerated); startup and shutdown events; the User-Agent;
the sign-in and RSVP pages; the service units; the OpenAPI realm; the
crate descriptions and the README, where it's set in bold.

Identifiers that are uppercase for their own reasons stay: INBUXA_*
settings, SUBSPACE_INBUXA. So do code comments and the AGPL 5(a) notice
lines.

Tests follow: the IMAP ID name, the default collection names, the PRODID
in the iTIP fixtures and the CalDAV free-busy expectations, and the e2e
legacy-protocol refusals. The webdav, imap and jmap suites pass, so do
the unit tests of every crate touched, and 73 of 75 SMTP tests; of the
other two, antispam fails on main too, and queue_retry is a timing flake
that passes on its own.

tests/resources/itip/rfc5546_todo.txt

@@ -32,7 +32,7 @@ summary.dtstart: Time(ItipTime { start: 867776400, tz_id: 32768 })
 summary.summary: Text("Create the requirements document")
 BEGIN:VCALENDAR
 METHOD:REQUEST
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 PRIORITY:1
@@ -57,7 +57,7 @@ END:VCALENDAR
 # Make sure B received the todo
 > get [email protected] [email protected]
 BEGIN:VCALENDAR
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 PRIORITY:1
@@ -103,7 +103,7 @@ summary.attendee: Participants([ItipParticipant { email: "[email protected]", name:
 summary.dtstart: Time(ItipTime { start: 867776400, tz_id: 32768 })
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 STATUS:IN-PROCESS
@@ -172,7 +172,7 @@ summary.attendee: Participants([ItipParticipant { email: "[email protected]", name:
 summary.dtstart: Time(ItipTime { start: 867776400, tz_id: 32768 })
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 PERCENT-COMPLETE:75
@@ -241,7 +241,7 @@ summary.attendee: Participants([ItipParticipant { email: "[email protected]", name:
 summary.dtstart: Time(ItipTime { start: 867776400, tz_id: 32768 })
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 DUE:19970722T170000Z
@@ -317,7 +317,7 @@ summary.summary: Text("Send Status Reports to Area Managers")
 ~summary.summary: Text("Create the requirements document")
 BEGIN:VCALENDAR
 METHOD:REQUEST
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 PRIORITY:1
@@ -347,7 +347,7 @@ summary.rrule: Rrule(ICalendarRecurrenceRule { freq: Monthly, until: None, count
 summary.summary: Text("Create the requirements document")
 BEGIN:VCALENDAR
 METHOD:CANCEL
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 STATUS:CANCELLED
@@ -367,7 +367,7 @@ END:VCALENDAR
 # Make sure "C" received the cancel request
 > get [email protected] [email protected]
 BEGIN:VCALENDAR
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 PRIORITY:1
@@ -451,7 +451,7 @@ summary.rrule: Rrule(ICalendarRecurrenceRule { freq: Monthly, until: None, count
 summary.summary: Text("Send Status Reports to Area Managers")
 BEGIN:VCALENDAR
 METHOD:REPLY
-PRODID:-//INBUXA//INBUXA Server//EN
+PRODID:-//inbuxa//inbuxa Server//EN
 VERSION:2.0
 BEGIN:VTODO
 PERCENT-COMPLETE:75