Add Dockerfile for deployment.

Dockerfile

@@ -0,0 +1,39 @@
+# syntax=docker/dockerfile:1
+
+# --- Stage 1: build the web frontend (web/dist) -----------------------------
+FROM node:22-bookworm-slim AS web
+WORKDIR /web
+# Install deps first for better layer caching. --include=dev is explicit so the
+# build works even if NODE_ENV=production leaks in (vite/tsc are devDependencies).
+COPY web/package.json web/package-lock.json ./
+RUN npm ci --include=dev
+COPY web/ ./
+RUN npm run build
+
+# --- Stage 2: build the Go server binary ------------------------------------
+FROM golang:1.25-bookworm AS go
+WORKDIR /src
+# Cache module downloads separately from the source.
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+# modernc.org/sqlite is pure Go, so we can build a fully static binary.
+RUN CGO_ENABLED=0 go build -trimpath -ldflags="-s -w" -o /out/server ./cmd/server
+
+# --- Stage 3: minimal runtime image -----------------------------------------
+FROM debian:bookworm-slim AS runtime
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+WORKDIR /app
+COPY --from=go /out/server /app/server
+COPY --from=web /web/dist /app/web/dist
+
+# The server reads these at runtime (see cmd/server/main.go). DATA_DIR should be
+# backed by a Dokku persistent volume so the SQLite DB survives redeploys.
+ENV STATIC_DIR=/app/web/dist \
+    DATA_DIR=/app/data \
+    PORT=8080
+EXPOSE 8080
+
+CMD ["/app/server"]