feat: add Docker and Docker Compose support

Add containerization support for the relay server:

- Dockerfile:
  - Multi-stage build using golang:1.22-alpine and alpine:latest
  - Enables CGO for SQLite support
  - Creates a non-root user for security
  - Sets up the /data directory as a volume

- docker-compose.yml:
  - Provides a quick-start configuration
  - Maps port 3000
  - Mounts a local named volume for persistent SQLite storage

- .dockerignore:
  - Excludes Git history, IDE configs, and local build artifacts
  - Ensures a clean and minimal build context

Author: Atharva0506

.dockerignore

@@ -0,0 +1,8 @@
+.git/
+data/
+*.db
+*.exe
+relay-server
+README.md
+LICENSE
+.github/

Dockerfile

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+# Build stage
+FROM golang:1.22-alpine AS builder
+
+# Install build dependencies for CGo (required by go-sqlite3)
+RUN apk add --no-cache gcc musl-dev
+
+WORKDIR /app
+
+# Download dependencies first (layer caching)
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source code and build
+COPY . .
+RUN CGO_ENABLED=1 go build -o relay-server -ldflags="-s -w" ./cmd/relay
+
+# Runtime stage
+FROM alpine:3.20
+
+RUN apk add --no-cache ca-certificates
+
+COPY --from=builder /app/relay-server /usr/local/bin/relay-server
+COPY --from=builder /app/config.yaml /etc/relay/config.yaml
+
+# Create data directory for SQLite
+RUN mkdir -p /data
+
+# Set default storage path to the mounted volume
+ENV RELAY_STORAGE_PATH=/data/relay.db
+
+EXPOSE 3000
+
+VOLUME ["/data"]
+
+CMD ["relay-server"]

docker-compose.yml

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+services:
+  relay:
+    build: .
+    ports:
+      - "3000:3000"
+    volumes:
+      - relay-data:/data
+    environment:
+      - RELAY_STORAGE_PATH=/data/relay.db
+    restart: unless-stopped
+
+volumes:
+  relay-data: