M9.R.42.4: bump install driver timeout 900s -> 1800s for Phase 5 rsync

The first M9.R.42 install run hit the 900s wall-time limit DURING
Phase 5 rsync (livesys -> /mnt), not on the Phase 2 sgdisk path
M9.R.41 documented.

Evidence (extracted from /tmp/m9r42_install.qcow2 by converting to
raw + sfdisk -d after the timeout-kill):

  /tmp/m9r42_install.raw1 : start=2048, size=1048576, type=esp (EF00)
  /tmp/m9r42_install.raw2 : start=1050624, size=66058207, type=8300

  EXT4-fs (vda2): mounted filesystem ... r/w  <-- Phase 3 line in
                                                  the kernel ring
  /tmp/m9r42_mnt: 542 MB of rsync'd live-root content visible
                                  (bin/ boot/ etc/ usr/ ...)

So:
  Phase 1 (hardware probe) OK
  Phase 2 (disk apply)     OK  <-- sgdisk + udev + EXT4 all clean
  Phase 3 (mount)          OK
  Phase 4 (install-root)   started, partial rsync
  Phase 5 (chroot setup)   not reached
  Phase 6 (boot install)   not reached

Bumping the timeout to 1800s (30 min) covers the worst-case rsync of
the M9.R.41 base-rootfs (~1.5 GB live-root squashfs unpacked).  No
behaviour change for fast hosts; the script still kills at the
timeout boundary.

This is the SAME shape as the M9.R.41 driver timeout bump that
covered the Phase 5 work — we just need more headroom now that the
M9.R.41-attributed Phase 2 race turns out to be a stale-binary
artifact (the M9.R.41.9 host /opt/repro/reprobuild/build/bin/repro
was never recompiled after the M9.R.41.9-12 reverts; my M9.R.42.1
fresh rebuild gave Phase 2 a clean run as documented in the M9.R.42
close-out evidence).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: zah

_m9r42_install.sh

@@ -18,7 +18,7 @@ ISO="${ISO:-/opt/repro/reprobuild/recipes/reproos-iso/build/reproos.iso}"
 DISK="${DISK:-/tmp/m9r42_install.qcow2}"
 DIAG_DISK="${DIAG_DISK:-/tmp/m9r42_diag.qcow2}"
 INSTALL_LOG="${INSTALL_LOG:-/tmp/m9r42_install.log}"
-INSTALL_TIMEOUT="${INSTALL_TIMEOUT:-900}"
+INSTALL_TIMEOUT="${INSTALL_TIMEOUT:-1800}"
 DIAG_OUT="${DIAG_OUT:-/tmp/m9r42_diag}"
 
 [ -f "$ISO" ] || { echo "ISO $ISO does not exist" >&2; exit 2; }