live-image: install stage tools and fail loudly if any are missing

The live image was still carrying the Phase 2 package list, so SMART,
CPUStress, and Network each hit a LookPath miss and returned
pass-with-skip. A run that skipped every real check still ended in
"completed" — nothing on the report said the image was broken.

Add smartmontools, stress-ng, fio, iperf3, lshw, lm-sensors,
e2fsprogs, and util-linux to mkosi.conf. Flip the three stages from
skip-pass to fail when their binary is missing so any future
packaging regression blocks the run instead of whispering past it.
Legitimate "no hardware" skips (no GPU, no hwmon, no disks,
non-destructive) are untouched.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

live-image/mkosi.conf

@@ -46,6 +46,17 @@ Packages=
     usbutils
     initramfs-tools
     zstd
+    # Stage binaries. Every package here backs a stage the agent runs —
+    # if any one goes missing the corresponding stage now fails the run
+    # (was: pass-with-skip). Keep this list in sync with agent/tests.
+    smartmontools
+    stress-ng
+    fio
+    iperf3
+    lshw
+    lm-sensors
+    e2fsprogs
+    util-linux
     # Firmware. firmware-linux-nonfree on bookworm is a thin metapackage
     # that does NOT pull i915 GuC/HuC — those live in firmware-misc-nonfree.
     # Enumerate explicitly so the blob for whatever hardware we boot on
@@ -59,7 +70,5 @@ Packages=
     amd64-microcode
     firmware-linux-nonfree
 
-# Phase 4 will add: smartmontools stress-ng fio iperf3 lshw lm-sensors
-
 [Host]
 # Copy the prebuilt Go agent in from the repo root via postinst.