Feat: Backend scaffolding and local dev stack

Backend/Dockerfile

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+# syntax=docker/dockerfile:1.7
+
+FROM golang:1.25.7-alpine AS base
+
+WORKDIR /app
+
+RUN apk add --no-cache ca-certificates curl git tzdata && update-ca-certificates
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+FROM base AS development
+
+RUN curl -fsSL https://raw.githubusercontent.com/air-verse/air/master/install.sh | sh -s -- -b /usr/local/bin
+
+COPY . .
+
+CMD ["air", "-c", ".air.web.toml"]
+
+FROM base AS builder
+
+ARG SERVICE_NAME=web
+
+COPY . .
+
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o /out/app ./cmd/${SERVICE_NAME}
+
+FROM alpine:3.22 AS runtime
+
+RUN apk add --no-cache ca-certificates tzdata && update-ca-certificates
+
+WORKDIR /app
+
+COPY --from=builder /out/app /usr/local/bin/app
+
+CMD ["/usr/local/bin/app"]