Use tmux for test runner — detachable SSH sessions

Tests now run inside a tmux session so you can disconnect and
reconnect without interrupting multi-hour test runs.

Changes:
- create-vm.sh: cloud-init no longer auto-runs tests, just provisions
  packages and clones the repo. Installs a `darkforge-test` command
  in /usr/local/bin that wraps run-in-vm.sh in tmux.
- run-in-vm.sh: detects when called as `darkforge-test` and re-execs
  inside a tmux session named "darkforge". --tmux flag for internal use.
- README updated with tmux workflow (detach/reattach instructions).

Workflow:
  ssh darkforge@<ip>
  darkforge-test --quick    # starts in tmux
  Ctrl+B D                  # detach, go do other things
  tmux attach -t darkforge  # come back later

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/proxmox/run-in-vm.sh

@@ -18,11 +18,33 @@
 #   10. Generates a JSON + text report
 #
 # Usage:
-#   bash run-in-vm.sh              # full run (2-6 hours depending on hardware)
-#   bash run-in-vm.sh --quick      # skip toolchain/kernel/ISO (30 min)
-#   bash run-in-vm.sh --no-build   # skip toolchain bootstrap (1 hour)
+#   darkforge-test                 # runs in tmux (detachable)
+#   darkforge-test --quick         # fast mode in tmux
+#   bash run-in-vm.sh              # direct run (2-6 hours)
+#   bash run-in-vm.sh --quick      # direct, skip toolchain/kernel/ISO (30 min)
+#   bash run-in-vm.sh --no-build   # direct, skip toolchain bootstrap (1 hour)
+#
+# tmux controls:
+#   Ctrl+B then D   — detach (tests keep running)
+#   tmux attach -t darkforge  — reattach
 # ============================================================================
 
+# --- If called as "darkforge-test", wrap in tmux ----------------------------
+TMUX_MODE=false
+for arg in "$@"; do
+    [ "$arg" = "--tmux" ] && TMUX_MODE=true
+done
+
+if [ "$TMUX_MODE" = false ] && [ "$(basename "$0")" = "darkforge-test" ]; then
+    # Re-exec ourselves inside a tmux session
+    ARGS="$*"
+    exec tmux new-session -d -s darkforge \
+        "bash $(readlink -f "$0") --tmux ${ARGS}; echo ''; echo 'Tests finished. Press Enter to close.'; read" \; \
+        attach-session -t darkforge
+fi
+# Strip --tmux from args for the actual test run
+set -- $(echo "$@" | sed 's/--tmux//g')
+
 set -uo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"