feat: Update devcontainer setup with Dockerfile and improved script for pre-commit hooks

.devcontainer/Dockerfile

@@ -0,0 +1,7 @@
+# .devcontainer/Dockerfile
+FROM mcr.microsoft.com/devcontainers/javascript-node:1-20-bullseye
+
+# CACHED INSTALLATION:
+# Install global NPM packages here. This creates a cached Docker layer.
+# We use 'su node' to ensure permissions are correct for the non-root user.
+RUN su node -c "npm install -g @google/gemini-cli"