fix: Docker build AVX issue with Node.js/Bun hybrid strategy

- Switch build stage from Bun to Node.js to avoid AVX CPU requirement
- Use Node.js 20 Alpine for building React client (Vite)
- Keep Bun runtime for API server (no AVX needed for runtime)
- Update README.md with build strategy and troubleshooting
- Update CLAUDE.md with Docker architecture documentation
- Add comprehensive docs/DOCKER_BUILD_FIX.md with technical details

Fixes #14 - Docker build crashes with "CPU lacks AVX support"

Tested:
- Docker build: SUCCESS
- Container runtime: SUCCESS
- Health check: PASS
- React client serving: PASS

CLAUDE.md

@@ -316,6 +316,13 @@ Missing (needs implementation):
 
 ### Docker Build and Run
 
+**Build Architecture**: The Dockerfile uses a hybrid approach to avoid AVX CPU requirements:
+
+- **Build stage** (Node.js 20): Builds React client with Vite (no AVX required)
+- **Runtime stage** (Bun 1.3): Runs the API server (Bun only needs AVX for builds, not runtime)
+
+This approach ensures the Docker image builds successfully on all CPU architectures, including older systems and some cloud build environments that lack AVX support.
+
 ```bash
 # Build the Docker image
 docker build -t ai-stack-deployer:latest .
@@ -331,6 +338,8 @@ docker run -d \
   ai-stack-deployer:latest
 ```
 
+**Note**: If you encounter "CPU lacks AVX support" errors during Docker builds, ensure you're using the latest Dockerfile which implements the Node.js/Bun hybrid build strategy.
+
 ### Deploying to Dokploy
 
 1. **Prepare Environment**: