Stop the boot from waiting on a black screen for the console to answer

About 1 boot in 10 of an installed system stops on a black screen at
"Starting Switch Root" until a key is pressed. systemd 257 and later
asks the console for its size with ANSI escape sequences when PID 1
starts and waits for the reply; with Plymouth holding the VT the reply
sometimes never comes.

Measured in QEMU on repeated boots of one install: 3 hangs in 30 and 1
in 40 on the prebuilt UKI, 7 in 40 on the stock initramfs, every one of
them ended by pressing Enter; none in 40 with a serial console, none in
40 with plymouth.enable=0, and none in 80 with
systemd.tty.term.console=dumb, which makes systemd skip the query.
systemd fixed two variants of this in v261; Arch's 261.2 still shows it.

The parameter goes where the last Plymouth boot fix went (3f725531,
initramfs_async=0): into the packaged omarchy-defaults.conf for fresh
installs, and a migration rebuilds the boot image on existing systems,
once per machine, only where the booted command line lacks it. Nothing
visible changes under "quiet splash".

Refs #2931

test/shell.d/limine-defaults-test.sh

@@ -10,6 +10,10 @@ grep -Fq 'KERNEL_CMDLINE[default]+=" initramfs_async=0"' "$packaged_defaults" ||
   fail "the packaged Limine defaults still unpack the initramfs synchronously"
 pass "packaged Limine defaults keep Plymouth alive at the LUKS prompt"
 
+grep -Fxq 'KERNEL_CMDLINE[default]+=" systemd.tty.term.console=dumb"' "$packaged_defaults" ||
+  fail "the packaged Limine defaults let PID 1 wait for the console to answer a size query"
+pass "packaged Limine defaults keep PID 1 from waiting on the console"
+
 grep -Fxq 'BOOT_ORDER="linux-t2, linux-omarchy, linux-omarchy-*, *, *fallback, Snapshots"' "$packaged_defaults" ||
   fail "packaged Limine defaults protect T2 Macs and prefer the exact Omarchy kernel elsewhere"
 pass "packaged Limine defaults protect T2 Macs and prefer the exact Omarchy kernel elsewhere"