ci: Consolidate back to 4 docker steps

- Remove separate build steps (didn't save time)
- Use original multi-stage Dockerfiles
- Delete unused Dockerfile.ci files
- 4 parallel docker builds + deploy

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/Dockerfile.ci

@@ -1,43 +0,0 @@
-# CI Dockerfile - assets pre-built in CI step
-# No npm install or build - just copy and run
-FROM node:22-slim
-
-# Build arguments for version info
-ARG APP_BUILD_VERSION=dev
-ARG APP_GIT_SHA=unknown
-ARG APP_BUILD_TIME=unknown
-
-ENV APP_BUILD_VERSION=${APP_BUILD_VERSION}
-ENV APP_GIT_SHA=${APP_GIT_SHA}
-ENV APP_BUILD_TIME=${APP_BUILD_TIME}
-
-# Install runtime dependencies only (Chromium for Puppeteer)
-RUN apt-get update && apt-get install -y \
-    curl \
-    chromium \
-    fonts-liberation \
-    libnss3 \
-    libxss1 \
-    libasound2 \
-    libatk-bridge2.0-0 \
-    libgtk-3-0 \
-    --no-install-recommends \
-    && rm -rf /var/lib/apt/lists/*
-
-ENV PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true
-ENV PUPPETEER_EXECUTABLE_PATH=/usr/bin/chromium
-
-WORKDIR /app
-
-# Copy pre-built assets from CI
-COPY backend/package*.json ./
-COPY backend/node_modules ./node_modules
-COPY backend/dist ./dist
-COPY backend/migrations ./migrations
-COPY backend/public/downloads ./public/downloads
-
-RUN mkdir -p /app/public/images/products
-
-EXPOSE 3010
-
-CMD ["node", "dist/index.js"]