Add Dockerfile and dockerignore for Cloud Run deployment

.dockerignore

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+.git
+creds/
+docs/
+sampledata/
+screenshots/
+Dockerfile
+LICENSE.md

Dockerfile

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+FROM golang:1.26 AS build
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 go build -o /heliosian .
+
+FROM gcr.io/distroless/static-debian12
+WORKDIR /app
+COPY --from=build /heliosian /app/heliosian
+COPY web /app/web
+ENTRYPOINT ["/app/heliosian"]