Allow install_python_stack to run on Colab

The _COLAB_NO_VENV flag was skipping both the PyPI version check
(which needs $VENV_DIR/bin/python) and install_python_stack (which
uses sys.executable and works fine without a venv). Decouple these:
guard only the version check with _COLAB_NO_VENV, so
install_python_stack runs normally on Colab.

studio/Unsloth_Studio_Colab.ipynb

@@ -64,11 +64,7 @@
     "id": "27e68f91"
    },
    "outputs": [],
-      "source": [
+   "source": "!git clone --depth 1 --branch main https://github.com/unslothai/unsloth.git\n%cd /content/unsloth\n!chmod +x studio/setup.sh && ./studio/setup.sh --local"
-        "!git clone --depth 1 --branch main https://github.com/unslothai/unsloth.git\n",
-        "%cd /content/unsloth\n",
-        "!chmod +x studio/setup.sh && ./studio/setup.sh"
-      ]
   },
   {
    "cell_type": "markdown",

studio/setup.sh

@@ -337,30 +337,20 @@ fast_install() {
 
 cd "$SCRIPT_DIR"
 
-# On Colab without a venv, skip all venv-dependent sections (Python deps
+# On Colab without a venv, skip venv-dependent Python deps sections but
-# update, llama.cpp build) -- the backend deps were already installed above.
+# continue to llama.cpp install so GGUF inference is available.
 if [ "$_COLAB_NO_VENV" = true ]; then
     echo "✅ Studio backend dependencies installed into system Python"
-
-    echo ""
-    echo "╔══════════════════════════════════════╗"
-    echo "║          Setup Complete!             ║"
-    echo "╠══════════════════════════════════════╣"
-    echo "║ Unsloth Studio is ready to start     ║"
-    echo "║ in your Colab notebook!              ║"
-    echo "║                                      ║"
-    echo "║ from colab import start              ║"
-    echo "║ start()                              ║"
-    echo "╚══════════════════════════════════════╝"
-    exit 0
 fi
 
 # ── Check if Python deps need updating ──
 # Compare installed package version against PyPI latest.
 # Skip all Python dependency work if versions match (fast update path).
-_PKG_NAME="${STUDIO_PACKAGE_NAME:-unsloth}"
+# On Colab (no venv), skip this version check (it needs $VENV_DIR/bin/python)
+# but still run install_python_stack below (it uses sys.executable).
 _SKIP_PYTHON_DEPS=false
-if [ "${SKIP_STUDIO_BASE:-0}" != "1" ] && [ "${STUDIO_LOCAL_INSTALL:-0}" != "1" ]; then
+_PKG_NAME="${STUDIO_PACKAGE_NAME:-unsloth}"
+if [ "$_COLAB_NO_VENV" != true ] && [ "${SKIP_STUDIO_BASE:-0}" != "1" ] && [ "${STUDIO_LOCAL_INSTALL:-0}" != "1" ]; then
     # Only check when NOT called from install.sh (which just installed the package)
     INSTALLED_VER=$("$VENV_DIR/bin/python" -c "
 from importlib.metadata import version