Fix three findings from final clean-pass audit

- apply.sh: gate sitecustomize.py install on backup success; a failed
  backup cp (disk full, read-only mount) previously fell through and
  overwrote the vendor file with no recovery path
- create_task.py: handle unexpected 2xx response schema in cmd_create;
  bare KeyError on result['id'] is replaced with a diagnostic print
- uninstall.sh: mv inside while loop had no error handling; under
  set -euo pipefail a failed mv aborted the script before rm -rf PATCH_DIR,
  leaving the system in partial-uninstall limbo

uninstall.sh

@@ -104,9 +104,12 @@ echo "Restoring UI bundle backup ..."
 RESTORED=0
 while IFS= read -r backup; do
     original="${backup%.pre-truecloud-patch}"
-    mv "$backup" "$original"
-    echo "  Restored: $original"
-    RESTORED=1
+    if mv "$backup" "$original"; then
+        echo "  Restored: $original"
+        RESTORED=1
+    else
+        echo "  WARNING: Could not restore $original — backup left at $backup"
+    fi
 # Keep these paths in sync with WEBUI_CANDIDATES in patch/patch_ui.py
 done < <(find /usr/share/truenas /usr/share/truenas-ui /var/www/truenas \
               -name "*.js.pre-truecloud-patch" 2>/dev/null)