chore: change port to 1234 and add Makefile/flake.nix

- Change dev server port from 1312 to 1234
- Add Makefile for common development commands
- Add flake.nix for Nix development environment

Makefile

@@ -0,0 +1,54 @@
+# Code Crispies - Interactive CSS Learning Platform
+
+.PHONY: help dev build test test-watch test-coverage format clean install deploy
+
+# Default port
+PORT = 1234
+
+help:
+	@echo "Code Crispies - Development Commands"
+	@echo ""
+	@echo "Development:"
+	@echo "  make dev          - Start dev server (port $(PORT))"
+	@echo "  make build        - Production build to dist/"
+	@echo ""
+	@echo "Testing:"
+	@echo "  make test         - Run tests once"
+	@echo "  make test-watch   - Run tests in watch mode"
+	@echo "  make test-coverage - Run tests with coverage"
+	@echo ""
+	@echo "Other:"
+	@echo "  make format       - Format all source files"
+	@echo "  make clean        - Remove build artifacts"
+	@echo "  make install      - Install dependencies"
+
+# Development
+dev:
+	npm start
+
+# Build
+build:
+	npm run build
+
+# Testing
+test:
+	npm run test
+
+test-watch:
+	npm run test.watch
+
+test-coverage:
+	npm run test.coverage
+
+# Formatting
+format:
+	npm run format
+	npm run format.lessons
+
+# Clean
+clean:
+	rm -rf dist/ node_modules/.vite/
+
+# Install
+install:
+	npm install