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.

entrypoint.sh

@@ -18,6 +18,9 @@
 #   PRINTER_NAME         CUPS queue name and advertised (DNS-SD) name.
 #   PRINTER_DESCRIPTION  CUPS Description (lpadmin -D) shown in the web UI.
 #   PPD_FILE             PPD used for the queue.
+#   PRINTER_OPTIONS      Space-separated PPD option assignments (key=value)
+#                        applied as queue defaults on every start, e.g.
+#                        "BRColorMode=Vivid TonerSaveMode=False".
 #   CERT_EXTRA_NAMES     Comma-separated extra DNS names / IP addresses to put
 #                        into the generated IPPS certificate (server SANs).
 #   CERT_DAYS            Validity of the generated certificate (default 3650).
@@ -29,6 +32,7 @@ PRINTER_URI="${PRINTER_URI:-}"
 PRINTER_PROTOCOL="${PRINTER_PROTOCOL:-socket}"
 PRINTER_DESCRIPTION="${PRINTER_DESCRIPTION:-}"
 PPD_FILE="${PPD_FILE:-/usr/share/cups/model/BR4150_2.PPD}"
+PRINTER_OPTIONS="${PRINTER_OPTIONS:-}"
 
 LOG_PREFIX="[entrypoint]"
 log() { echo "${LOG_PREFIX} $*"; }
@@ -331,6 +335,50 @@ if lpstat -p "${PRINTER_NAME}" >/dev/null 2>&1; then
     log "queue ${PRINTER_NAME} is shared and set as default"
 fi
 
+# Apply optional queue defaults from PRINTER_OPTIONS (see README). Runs on every
+# start so the settings survive the (re)creation of the queue; an unusable entry
+# only logs a warning instead of aborting the startup ("set -eu"). Names and
+# values are checked against the queue's options first, because lpadmin would
+# happily store unknown assignments as queue defaults.
+apply_printer_options() {
+    [ -n "${PRINTER_OPTIONS}" ] || return 0
+    if ! lpstat -p "${PRINTER_NAME}" >/dev/null 2>&1; then
+        log "warning: queue ${PRINTER_NAME} does not exist; skipping PRINTER_OPTIONS"
+        return 0
+    fi
+    ppd_options="$(lpoptions -p "${PRINTER_NAME}" -l 2>/dev/null || true)"
+    for opt in ${PRINTER_OPTIONS}; do
+        case "${opt}" in
+            ?*=*) ;;
+            *)
+                log "warning: ignoring malformed PRINTER_OPTIONS entry '${opt}' (expected key=value)"
+                continue
+                ;;
+        esac
+        name="${opt%%=*}"
+        value="${opt#*=}"
+        line="$(printf '%s\n' "${ppd_options}" | grep "^${name}/")" || {
+            log "warning: PPD has no option '${name}'; ignoring (names/values: 'lpoptions -p ${PRINTER_NAME} -l')"
+            continue
+        }
+        # Option lines look like "Name/Text: value1 value2 ..." ('*' = default).
+        values="$(printf '%s\n' "${line#*: }" | tr ' ' '\n' | sed 's/^\*//')"
+        if ! printf '%s\n' "${values}" | grep -qxF "${value}" \
+                && ! { case "${value}" in Custom.*)
+                        printf '%s\n' "${values}" | grep -q 'Custom\.'
+                        ;; *) false ;; esac; }; then
+            log "warning: PPD option '${name}' has no value '${value}'; ignoring"
+            continue
+        fi
+        if lpadmin -p "${PRINTER_NAME}" -o "${opt}" >/dev/null 2>&1; then
+            log "queue default ${opt} applied"
+        else
+            log "warning: lpadmin -o ${opt} failed; ignoring"
+        fi
+    done
+}
+apply_printer_options
+
 # --- Verify CUPS is reachable on the network --------------------------------
 # cupsd also runs with nothing but its domain socket, e.g. when it cannot bind
 # the privileged port 631 (rootless Podman with host networking). It then still