feat(frontend): Add Docker containerization support for development and production

Implement complete Docker setup for Next.js 16 frontend with multi-stage builds,
hot reload support, and production optimizations.

Changes:
- Add Dockerfile with multi-stage build (deps, builder, development, production)
- Add .dockerignore to exclude unnecessary files from Docker context
- Add .env.local.example template for environment configuration
- Update next.config.ts with standalone output for production builds
- Add Docker convenience scripts to package.json for easy container management
- Support hot reload in development with volume mounts
- Use Node.js 20 Alpine for smaller image size
- Implement security best practices (non-root user in production)

Technical Details:
- Development stage: Full source mounted with hot reload via Turbopack
- Production stage: Standalone build with optimized static assets
- Image size: ~1.17GB (development), smaller for production
- Port: 3000 (maps to container port 3000)

Testing:
- Docker build verified for development target
- Container startup successful with Next.js 16.0.1
- HTTP 200 response confirmed on localhost:3000
- Hot reload functional with volume mounts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

.env.local.example

@@ -0,0 +1,47 @@
+# ColaFlow Frontend Environment Variables Template
+# Copy this file to .env.local and modify the values as needed
+
+# ============================================
+# Backend API Configuration
+# ============================================
+NEXT_PUBLIC_API_URL=http://localhost:5000
+
+# SignalR Hub Configuration
+NEXT_PUBLIC_SIGNALR_HUB_URL=http://localhost:5000/hubs/notifications
+NEXT_PUBLIC_WS_URL=ws://localhost:5000/hubs/project
+
+# Internal API URL (for server-side calls in Docker)
+API_URL=http://backend:8080
+
+# ============================================
+# Application Configuration
+# ============================================
+NEXT_PUBLIC_APP_NAME=ColaFlow
+NEXT_PUBLIC_APP_DESCRIPTION=AI-powered project management system with MCP integration
+
+# ============================================
+# Feature Flags
+# ============================================
+# Enable analytics tracking
+NEXT_PUBLIC_ENABLE_ANALYTICS=false
+
+# Enable debug mode (shows additional logging)
+NEXT_PUBLIC_ENABLE_DEBUG=true
+
+# ============================================
+# Development Configuration (Optional)
+# ============================================
+# Port for Next.js dev server
+# PORT=3000
+
+# Node environment
+# NODE_ENV=development
+
+# ============================================
+# Production Configuration (Optional)
+# ============================================
+# NEXT_PUBLIC_API_URL=https://api.colaflow.com
+# NEXT_PUBLIC_SIGNALR_HUB_URL=https://api.colaflow.com/hubs/notifications
+# NEXT_PUBLIC_WS_URL=wss://api.colaflow.com/hubs/project
+# NEXT_PUBLIC_ENABLE_ANALYTICS=true
+# NEXT_PUBLIC_ENABLE_DEBUG=false