run deb package pip install stage as navidrome-uploader user instead of root

debian/navidrome-uploader.postinst

@@ -3,12 +3,15 @@ set -e
 
 APP_DIR="/opt/navidrome-uploader"
 VENV_DIR="${APP_DIR}/venv"
+APP_USER="navidrome-uploader"
 
 case "$1" in
   configure)
-        python3 -m venv "${VENV_DIR}"
-        "${VENV_DIR}/bin/pip" install --no-cache-dir --upgrade pip
-        "${VENV_DIR}/bin/pip" install --no-cache-dir -r "${APP_DIR}/requirements.txt"
+    chown -R "$APP_USER:$APP_USER" "$APP_DIR"
+
+    runuser -u "$APP_USER" -- python3 -m venv "$VENV_DIR"
+    runuser -u "$APP_USER" -- "$VENV_DIR/bin/pip" install --no-cache-dir --upgrade pip
+    runuser -u "$APP_USER" -- "$VENV_DIR/bin/pip" install --no-cache-dir -r "$APP_DIR/requirements.txt"
 
     if command -v systemctl >/dev/null 2>&1; then
       systemctl daemon-reload || true
@@ -20,3 +23,4 @@ esac
 
 exit 0
 
+