fix(stirling-pdf): install unoserver on the system python, and append to .env (#16439)

install/stirling-pdf-install.sh

@@ -34,7 +34,11 @@ msg_ok "Installed Dependencies"
 PYTHON_VERSION="3.12" setup_uv
 JAVA_VERSION="25" setup_java
 
-read -r -p "${TAB3}Do you want to use Stirling-PDF with Login? (no/n = without Login) [Y/n] " response
+if ! read -r -p "${TAB3}Do you want to use Stirling-PDF with Login? (no/n = without Login) [Y/n] " response; then
+  # No interactive stdin (EOF): fall back to the no-login install instead of
+  # silently selecting login, which the -z test below would otherwise do.
+  response="n"
+fi
 response=${response,,} # Convert to lowercase
 login_mode="false"
 if [[ "$response" == "y" || "$response" == "yes" || -z "$response" ]]; then
@@ -72,7 +76,10 @@ $STD uv pip install \
   pillow \
   pdf2image
 $STD apt install -y python3-uno python3-pip
-$STD pip3 install --break-system-packages --timeout=120 unoserver
+# Install unoserver for the system Python, not the venv activated above: `uno` is
+# provided by python3-uno for /usr/bin/python3 only, and unoserver.service expects
+# /usr/local/bin/unoserver. A bare `pip3` here resolves to the venv's pip.
+$STD /usr/bin/python3 -m pip install --break-system-packages --timeout=120 unoserver
 ln -sf /opt/.venv/bin/python3 /usr/local/bin/python3
 ln -sf /opt/.venv/bin/pip /usr/local/bin/pip
 msg_ok "Installed Python Dependencies"
@@ -104,7 +111,7 @@ PATH=/opt/.venv/bin:/usr/lib/libreoffice/program:/usr/local/sbin:/usr/local/bin:
 EOF
 
 if [[ "$login_mode" == "true" ]]; then
-  cat <<EOF >/opt/Stirling-PDF/.env
+  cat <<EOF >>/opt/Stirling-PDF/.env
 # activate Login
 DISABLE_ADDITIONAL_FEATURES=false
 SECURITY_ENABLELOGIN=true