fix: Refactor devcontainer to use base Ubuntu with Docker-in-Docker

- Switch from docker-compose service to base Ubuntu container
- Add Docker-in-Docker to run docker-compose inside Codespace
- This provides git access and full dev environment
- Superset services run via docker-compose from within the container

.devcontainer/setup-dev.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+# Setup script for Superset Codespaces development environment
+
+set -e
+
+echo "🔧 Setting up Superset development environment..."
+
+# Install additional system dependencies
+echo "📦 Installing system dependencies..."
+sudo apt-get update
+sudo apt-get install -y \
+    build-essential \
+    libssl-dev \
+    libffi-dev \
+    libsasl2-dev \
+    libldap2-dev \
+    libpq-dev \
+    python3-pip \
+    python3-venv
+
+# Make the start script executable
+chmod +x .devcontainer/start-superset.sh
+
+echo "✅ Development environment setup complete!"
+echo "🚀 Run '.devcontainer/start-superset.sh' to start Superset"