ci: add Docker build and GitHub Container Registry workflow

Add complete Docker containerization and CI/CD setup:

Docker Configuration:
- Multi-stage Dockerfile with 3 stages (deps, builder, runner)
- Stage 1: Install dependencies with pnpm in Alpine
- Stage 2: Build Next.js static export
- Stage 3: Serve static files with nginx:alpine
- Health check endpoint on /health
- Optimized for production with layer caching

Nginx Configuration:
- Custom nginx.conf for static file serving
- Gzip compression enabled
- Security headers (X-Frame-Options, X-Content-Type-Options, etc.)
- Static asset caching with 1-year expiry
- Client-side routing support (try_files)
- Health check endpoint for container orchestration
- Error page handling

GitHub Workflow (docker-build-push.yml):
- Triggers on push to main, tags, and pull requests
- Multi-platform builds (linux/amd64, linux/arm64)
- Pushes to GitHub Container Registry (ghcr.io)
- Automatic tagging: latest, semver, sha, branch
- Uses GitHub Actions cache for faster builds
- Requires only GITHUB_TOKEN (no secrets needed)

.dockerignore:
- Excludes node_modules, .next, build artifacts
- Excludes dev files, logs, and IDE configs
- Keeps Docker image size minimal

Image will be available at:
ghcr.io/valknarness/units-ui:latest

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

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

.dockerignore

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+# Dependencies
+node_modules
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# Next.js
+.next
+out
+
+# Production
+build
+dist
+
+# Misc
+.DS_Store
+*.pem
+
+# Debug
+*.log
+
+# Local env files
+.env*.local
+.env
+
+# Vercel
+.vercel
+
+# TypeScript
+*.tsbuildinfo
+next-env.d.ts
+
+# Git
+.git
+.gitignore
+
+# IDE
+.vscode
+.idea
+*.swp
+*.swo
+
+# Testing
+coverage
+.nyc_output
+
+# Turbopack
+.turbo
+
+# Documentation
+README.md
+IMPLEMENTATION_PLAN.md

.github/workflows/docker-build-push.yml

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+name: Build and Push Docker Image
+
+on:
+  push:
+    branches:
+      - main
+    tags:
+      - 'v*'
+  pull_request:
+    branches:
+      - main
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata (tags, labels) for Docker
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+            type=sha,prefix={{branch}}-
+            type=raw,value=latest,enable={{is_default_branch}}
+
+      - name: Build and push Docker image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          platforms: linux/amd64,linux/arm64
+
+      - name: Image digest
+        run: echo ${{ steps.meta.outputs.digest }}

Dockerfile

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+# Multi-stage Dockerfile for Next.js 16 static export
+
+# Stage 1: Dependencies
+FROM node:22-alpine AS deps
+RUN apk add --no-cache libc6-compat
+WORKDIR /app
+
+# Install pnpm
+RUN corepack enable && corepack prepare pnpm@latest --activate
+
+# Copy package files
+COPY package.json pnpm-lock.yaml ./
+
+# Install dependencies
+RUN pnpm install --frozen-lockfile
+
+# Stage 2: Builder
+FROM node:22-alpine AS builder
+WORKDIR /app
+
+# Install pnpm
+RUN corepack enable && corepack prepare pnpm@latest --activate
+
+# Copy dependencies from deps stage
+COPY --from=deps /app/node_modules ./node_modules
+
+# Copy source code
+COPY . .
+
+# Build the application (static export)
+RUN pnpm build
+
+# Stage 3: Runner (serve static files)
+FROM nginx:alpine AS runner
+
+# Copy custom nginx config
+COPY --from=builder /app/nginx.conf /etc/nginx/nginx.conf
+
+# Copy static files from build
+COPY --from=builder /app/out /usr/share/nginx/html
+
+# Expose port 80
+EXPOSE 80
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
+  CMD wget --no-verbose --tries=1 --spider http://localhost/ || exit 1
+
+# Start nginx
+CMD ["nginx", "-g", "daemon off;"]

nginx.conf

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+events {
+  worker_connections 1024;
+}
+
+http {
+  include /etc/nginx/mime.types;
+  default_type application/octet-stream;
+
+  # Logging
+  access_log /var/log/nginx/access.log;
+  error_log /var/log/nginx/error.log;
+
+  # Performance
+  sendfile on;
+  tcp_nopush on;
+  tcp_nodelay on;
+  keepalive_timeout 65;
+  types_hash_max_size 2048;
+
+  # Gzip compression
+  gzip on;
+  gzip_vary on;
+  gzip_min_length 1024;
+  gzip_types text/plain text/css text/xml text/javascript application/x-javascript application/xml+rss application/json application/javascript;
+
+  server {
+    listen 80;
+    server_name localhost;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+    add_header Referrer-Policy "no-referrer-when-downgrade" always;
+
+    # Cache static assets
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
+      expires 1y;
+      add_header Cache-Control "public, immutable";
+    }
+
+    # Next.js static files
+    location /_next/static/ {
+      expires 1y;
+      add_header Cache-Control "public, immutable";
+    }
+
+    # Handle client-side routing
+    location / {
+      try_files $uri $uri.html $uri/ /index.html;
+    }
+
+    # Health check endpoint
+    location /health {
+      access_log off;
+      return 200 "healthy\n";
+      add_header Content-Type text/plain;
+    }
+
+    # Error pages
+    error_page 404 /404.html;
+    error_page 500 502 503 504 /50x.html;
+  }
+}