build: update Dockerfile with tests and multi-stage build, add Makefile

- Dockerfile runs go test before building
- Multi-stage: build+test stage, minimal alpine final image
- Add gcc/musl-dev for CGO (sqlite)
- Trim binaries with -s -w ldflags
- Makefile with build, test, clean, docker targets
- Version injection via ldflags

Dockerfile

@@ -1,15 +1,25 @@
 # Build stage
 FROM golang:1.24-alpine AS builder
 WORKDIR /src
-RUN apk add --no-cache make
+RUN apk add --no-cache make gcc musl-dev
+
 COPY go.mod go.sum ./
 RUN go mod download
-COPY . .
-RUN go build -o /chatd ./cmd/chatd/
-RUN go build -o /chat-cli ./cmd/chat-cli/
 
-# Final stage
-FROM alpine:latest
+COPY . .
+
+# Run tests
+ENV DBURL="file::memory:?cache=shared"
+RUN go test ./...
+
+# Build binaries
+RUN CGO_ENABLED=1 go build -trimpath -ldflags="-s -w" -o /chatd ./cmd/chatd/
+RUN CGO_ENABLED=1 go build -trimpath -ldflags="-s -w" -o /chat-cli ./cmd/chat-cli/
+
+# Final stage — server only
+FROM alpine:3.21
+RUN apk add --no-cache ca-certificates
 COPY --from=builder /chatd /usr/local/bin/chatd
+
 EXPOSE 8080
-CMD ["chatd"]
+ENTRYPOINT ["chatd"]