fix(run.sh): add check for python3-venv and provide instructions

scripts/run.sh

@@ -2,6 +2,24 @@
 # Exit immediately if a command exits with a non-zero status.
 set -e
 
+# --- Prerequisite check for python3-venv ---
+echo "Checking for Python venv module..."
+if ! python3 -c 'import venv' &> /dev/null; then
+    echo "Python 'venv' module is missing. It's required to create a virtual environment for the backend."
+
+    # Attempt to provide specific installation instructions
+    if command -v apt &> /dev/null; then
+        PY_VERSION_SHORT=$(python3 -c 'import sys; print(f"{sys.version_info.major}.{sys.version_info.minor}")')
+        echo "It seems you are on a Debian/Ubuntu-based system. Please install the venv module by running:"
+        echo "sudo apt update && sudo apt install python${PY_VERSION_SHORT}-venv"
+    else
+        echo "Please install the Python 'venv' module for your system."
+    fi
+
+    exit 1
+fi
+echo "Python venv module found."
+
 # --- Backend Setup ---
 echo "Setting up backend..."
 cd backend