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

patch/apply.sh

@@ -85,17 +85,24 @@ if [ -z "$SITE_PKG" ]; then
     echo "  Run: $PYTHON -c \"import site; print(site.getsitepackages())\""
 else
     # Back up any pre-existing sitecustomize.py that isn't ours.
+    _can_install=true
     if [ -f "$SITE_PKG/sitecustomize.py" ] && \
        ! grep -q "truecloud-patch" "$SITE_PKG/sitecustomize.py" 2>/dev/null; then
-        cp "$SITE_PKG/sitecustomize.py" \
-           "$SITE_PKG/sitecustomize.py.pre-truecloud-patch"
-        echo "OK: Backed up existing sitecustomize.py"
+        if cp "$SITE_PKG/sitecustomize.py" \
+              "$SITE_PKG/sitecustomize.py.pre-truecloud-patch"; then
+            echo "OK: Backed up existing sitecustomize.py"
+        else
+            echo "WARNING: Could not back up existing sitecustomize.py; skipping install to avoid data loss."
+            _can_install=false
+        fi
     fi
 
-    if cp "$PATCH_DIR/sitecustomize.py" "$SITE_PKG/sitecustomize.py" 2>/dev/null; then
-        echo "OK: Installed sitecustomize.py → $SITE_PKG/sitecustomize.py"
-    else
-        echo "WARNING: Failed to write $SITE_PKG/sitecustomize.py (permission error?)"
+    if $_can_install; then
+        if cp "$PATCH_DIR/sitecustomize.py" "$SITE_PKG/sitecustomize.py" 2>/dev/null; then
+            echo "OK: Installed sitecustomize.py → $SITE_PKG/sitecustomize.py"
+        else
+            echo "WARNING: Failed to write $SITE_PKG/sitecustomize.py (permission error?)"
+        fi
     fi
 fi