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

Dockerfile

@@ -1,22 +1,25 @@
-# Use official Bun image
 # ***NEVER FORGET THE PRINCIPLES RULES***
-FROM oven/bun:1.3-alpine AS base
 
-# Set working directory
+# Build stage - Use Node.js to avoid AVX CPU requirement
+FROM node:20-alpine AS builder
+
 WORKDIR /app
 
-# Copy package files
 COPY package.json bun.lock* ./
 
-# Install dependencies
-FROM base AS deps
-RUN bun install --frozen-lockfile --production
+# Install dependencies using npm (works without AVX)
+RUN npm install
 
-# Build stage
-FROM base AS builder
-RUN bun install --frozen-lockfile
 COPY . .
-RUN bun run build
+
+# Client: Vite build via Node.js
+# API: Skip bun build, copy src files directly (Bun will run them at runtime)
+RUN npm run build:client
+
+FROM node:20-alpine AS deps
+WORKDIR /app
+COPY package.json bun.lock* ./
+RUN npm install --production
 
 # Production stage
 FROM oven/bun:1.3-alpine AS runner