Add an integration test suite that boots ISO scenarios in QEMU (#109)

* Move the unit tests under test/unit

test/ is growing an integration suite; the fast, VM-free tests get their
own directory so the two kinds cannot be confused. test/all keeps its
role as the aggregate runner for everything that needs no built ISO.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Add an integration suite that boots ISO scenarios in QEMU

test/integration installs an ISO once — unattended, from a generated
cidata drive — and saves a reusable base image; each scenario in
test/integration.d/ then boots a throwaway overlay with its own copy of
the firmware vars. Shared machinery (VM lifecycle, QMP screendump + OCR
console driving, virtual keystrokes, guest SSH, the cidata build) lives
in base-test.sh, so a new scenario is one file.

The first scenario proves omarchy-system-factory-reset hands a machine
on without destroying a shared ESP: a Windows entry and a foreign Linux
with its own machine-id, boot directory, and UKIs must survive both the
staged reset and the first-boot provisioning that follows.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Let omarchy-iso-make keep the host package cache

Purging /var/cache/pacman/pkg needs interactive sudo, which blocks
unattended builds. --keep-pkg-cache skips the purge so test rigs and
agents can build an ISO without a prompt.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

test/all

@@ -1,13 +1,16 @@
 #!/bin/bash
+#
+# Fast, VM-free tests only. The integration scenarios that boot the ISO in
+# QEMU live in test/integration.d/ and run via ./test/integration.
 
 set -euo pipefail
 
 ROOT=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)
 
-for test in "$ROOT"/test/*-test.sh; do
+for test in "$ROOT"/test/unit/*-test.sh; do
   printf '==> %s\n' "${test#$ROOT/}"
   bash "$test"
 done
 
-printf '==> test/test_*.py\n'
-python3 -m unittest discover -t "$ROOT" -s "$ROOT/test"
+printf '==> test/unit/test_*.py\n'
+python3 -m unittest discover -t "$ROOT" -s "$ROOT/test/unit"