Stop the live installer crashing the kernel on pre-T2 Macs

The ISO boots linux-t2 on every machine. On a MacBookPro11,4 applesmc finds the
SMC and then takes a NULL pointer dereference registering the keyboard-backlight
LED, in led_trigger_set_default -> queue_work_on.

The udev worker dies mid-init holding locks and the damage spreads: reading the
half-registered LED blocks systemd-backlight, opening /dev/rfkill blocks iwd
while it holds the global misc_mtx, and every later misc device open blocks
behind that mutex. LVM opens one, so the install stops at "Cleaning up existing
holders on install disk" and never resumes — no error, no progress, nothing to
see.

Nothing in the installer needs the SMC. It reads sensors and drives the fans and
keyboard backlight, and the firmware manages the fans by itself; the installed
system still loads applesmc normally. Blacklisting it in the live environment
only, alongside the Panther Lake audio blacklist that exists for the same class
of problem.

Extracted from #102, which also carried an unrelated rework of the disk probes.

Co-Authored-By: cupatea <vladyslav@hey.com>
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

configs/airootfs/etc/modprobe.d/blacklist-applesmc.conf

@@ -0,0 +1,3 @@
+# linux-t2 ships for every machine, and on a pre-T2 Mac its applesmc oopses
+# registering the keyboard-backlight LED, wedging udev. Nothing here needs the SMC.
+blacklist applesmc