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

README.md

@@ -36,13 +36,16 @@ User's AI Stack Container (OpenCode + ttyd)
 
 ### Technology Stack
 
-- **Runtime**: Bun 1.3+
+- **Runtime**: Bun 1.3+ (production), Node.js 20 (build)
 - **Framework**: Hono 4.11.3
 - **Language**: TypeScript
-- **Container**: Docker with multi-stage builds
+- **Frontend**: React 19 + Vite + Tailwind CSS 4
+- **Container**: Docker with multi-stage builds (Node.js build, Bun runtime)
 - **Orchestration**: Dokploy
 - **Reverse Proxy**: Traefik with wildcard SSL
 
+**Build Strategy**: Uses Node.js for building (avoids AVX CPU requirement) and Bun for runtime (performance).
+
 ## Quick Start
 
 ### Prerequisites
@@ -344,6 +347,24 @@ If a deployment fails but the name is marked as taken:
 2. Delete the partial deployment if present
 3. Try deployment again
 
+### Docker Build Fails with "CPU lacks AVX support"
+
+**Error**: `panic(main thread): Illegal instruction at address 0x...`
+
+**Cause**: Bun requires AVX CPU instructions which may not be available in all Docker build environments.
+
+**Solution**: Already implemented in Dockerfile. The build uses Node.js (no AVX requirement) for building and Bun for runtime:
+
+```dockerfile
+FROM node:20-alpine AS builder
+RUN npm install
+RUN npm run build:client
+
+FROM oven/bun:1.3-alpine AS runner
+```
+
+If you see this error, ensure you're using the latest Dockerfile from the repository.
+
 ## Security Notes
 
 - All API tokens stored in environment variables (never in code)