chore(deploy): Dockerfile + Dockge compose + deploy guide

Dockerfile

@@ -0,0 +1,32 @@
+# Flashcard — single-container production image.
+# Runs the Express API and serves the built React frontend on PORT (default 3000).
+#
+# The backend is launched with tsx (TypeScript runtime) because the shared
+# package is consumed as TypeScript source; this matches how the app runs in dev
+# and avoids a separate compile step for the shared workspace.
+FROM node:22-bookworm-slim
+
+# better-sqlite3 is a native module. Provide a toolchain in case no prebuilt
+# binary exists for the target platform (most amd64/arm64 hosts use a prebuild).
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends python3 make g++ ca-certificates \
+  && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+# Install dependencies first for better layer caching.
+# Do NOT set NODE_ENV=production here: the image needs devDependencies
+# (vite to build the frontend, tsx to run the backend).
+COPY package.json package-lock.json ./
+COPY packages/shared/package.json packages/shared/package.json
+COPY packages/backend/package.json packages/backend/package.json
+COPY packages/frontend/package.json packages/frontend/package.json
+RUN npm ci
+
+# Copy the source and build the static frontend (served by the backend).
+COPY . .
+RUN npm -w @flashcard/frontend run build \
+  && chmod +x /app/docker-entrypoint.sh
+
+EXPOSE 3000
+ENTRYPOINT ["/app/docker-entrypoint.sh"]