feat: add multi-stage Dockerfile and docker-compose.yml

- Multi-stage Dockerfile: golang:1.24-alpine builder → alpine:3.21 runtime
  - CGO_ENABLED=0 for static binary, stripped with -ldflags="-s -w"
  - Only copies ca-certificates and tzdata to runtime image
  - Config via volume mount at /etc/gosearch/config.toml
- docker-compose.yml: gosearch + Valkey 8
  - Valkey healthcheck ensures gosearch starts after cache is ready
  - Persistent Valkey volume
  - config.toml mounted read-only
- Update .gitignore with Go build artifacts

Dockerfile

@@ -0,0 +1,27 @@
+# Build stage
+FROM golang:1.24-alpine AS builder
+
+RUN apk add --no-cache git
+
+WORKDIR /src
+
+# Cache module downloads
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source and build
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-s -w" -o /gosearch ./cmd/searxng-go
+
+# Runtime stage
+FROM alpine:3.21
+
+RUN apk add --no-cache ca-certificates tzdata
+
+COPY --from=builder /gosearch /usr/local/bin/gosearch
+COPY config.example.toml /etc/gosearch/config.example.toml
+
+EXPOSE 8080
+
+ENTRYPOINT ["gosearch"]
+CMD ["-config", "/etc/gosearch/config.toml"]