feat: Docker, docker-compose, and deployment config (Task 13)

- Dockerfile: two-stage build (builder installs all deps + vite build; runtime copies dist + server)
- docker-compose.yml: 127.0.0.1:3004:8080, named volume for SQLite, env var interpolation
- .env.example: all required environment variables documented
- .dockerignore: exclude node_modules, dist, data, .env from build context
- vite.config.ts: outDir → ../client/dist, /api proxy to :3001 for dev
- .gitignore: remove Docker entries (files should be tracked for deployment)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,24 @@
+# --- Build stage ---
+FROM node:20-alpine AS builder
+WORKDIR /app
+RUN apk add --no-cache python3 make g++
+COPY package.json package-lock.json* ./
+RUN npm install --no-audit --no-fund
+COPY . .
+RUN npm run build
+
+# --- Runtime stage ---
+FROM node:20-alpine
+ENV NODE_ENV=production PORT=8080
+WORKDIR /app
+RUN apk add --no-cache python3 make g++
+COPY package.json package-lock.json* ./
+RUN npm install --omit=dev --no-audit --no-fund
+COPY --from=builder /app/client/dist ./client/dist
+COPY server/ ./server/
+RUN mkdir -p /app/data && chown -R node:node /app
+USER node
+EXPOSE 8080
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+  CMD wget -q --spider http://localhost:8080/ || exit 1
+CMD ["node", "server/server.js"]