fix pale colours and map driverless print options

Set *DefaultBRColorMode: None in the vendor PPD so every job sends
<</UseCIEColor false>>: Brother's Normal/Vivid modes enable the printer's
own CIE conversion, which washed the colours out.

Add six APPrinterPreset entries mapping print-color-mode and
print-quality from driverless (AirPrint/IPP) clients onto the Brother
device options; they use the notation CUPS generates itself (Apple
metadata as 'key value' pairs, PPD options as '*Name Value'), because
key=value strings are silently discarded. print-quality is 3/4/5.

Add the PRINTER_OPTIONS env var: whitespace-separated key=value pairs
applied as queue defaults on every start via lpadmin -o, validated
against the queue's PPD, with warnings instead of a failed startup.

Document all of it in the README. The VividNoCIE candidate was dropped
after test prints showed no difference from None. Archive the OpenSpec
change and sync the printserver/cups spec with the two new
requirements.

openspec/changes/archive/2026-10-20-fix-colour-defaults-and-client-options/.openspec.yaml

@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-10-20