Add kill switch and recover.sh for emergency recovery

If the patch ever prevents middlewared from starting, users now have a
clear escape hatch that requires no knowledge of Python internals:

  bash /data/truecloud-patch/recover.sh

Or at a bare shell prompt:

  touch /data/truecloud-patch/disabled
  systemctl restart middlewared

sitecustomize.py checks for /data/truecloud-patch/disabled at Python
startup and skips the import hook entirely when the file exists.
apply.sh does the same so the PREINIT script also does nothing on reboot.

recover.sh is copied to /data/truecloud-patch/ by install.sh so it is
available even without the original repo directory.

README gains an "Emergency recovery" section above Troubleshooting.

recover.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+# recover.sh — emergency recovery if middlewared won't start after installing truecloud-patch.
+#
+# Run this from the TrueNAS shell (local console, SSH, or debug shell):
+#
+#   bash /data/truecloud-patch/recover.sh
+#
+# What it does:
+#   1. Creates /data/truecloud-patch/disabled  — sitecustomize.py checks for this
+#      file at startup and skips the import hook entirely, so middlewared starts
+#      clean without any of our code running.
+#   2. Restarts middlewared.
+#
+# To re-enable the patch after investigating:
+#   rm /data/truecloud-patch/disabled
+#   bash /data/truecloud-patch/apply.sh
+
+PATCH_DIR="/data/truecloud-patch"
+
+if [ "$(id -u)" -ne 0 ]; then
+    echo "ERROR: must be run as root." >&2
+    exit 1
+fi
+
+if [ ! -d "$PATCH_DIR" ]; then
+    echo "ERROR: $PATCH_DIR not found — truecloud-patch may not be installed." >&2
+    exit 1
+fi
+
+touch "$PATCH_DIR/disabled"
+echo "Kill switch set: $PATCH_DIR/disabled created."
+echo "Restarting middlewared ..."
+systemctl restart middlewared
+echo ""
+echo "middlewared restarted without the truecloud-patch hook."
+echo "Your system should be back to normal (Storj-only TrueCloud Backup)."
+echo ""
+echo "To re-enable the patch once you have investigated:"
+echo "  rm $PATCH_DIR/disabled"
+echo "  bash $PATCH_DIR/apply.sh"