✨ feat(deploy): Dockerfile + Helm chart for k3s homelab deployment

Pattern adapted from arcodange-org/webapp.

Degraded mode : no DB / no SMTP / no Vault yet, just serves the binary +
swagger + healthz. Subsequent PRs will add Vault auth + Postgres dynamic
credentials + SMTP config.

Ingress route : dancecoachlessons.arcodange.lab (homelab internal).

Dockerfile

@@ -0,0 +1,36 @@
+# Build dance-lessons-coach Docker image
+FROM golang:1.26-alpine AS builder
+
+# Install git (required for go mod download)
+RUN apk add --no-cache git
+
+# Set working directory
+WORKDIR /app
+
+# Copy go module files and download dependencies
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy entire source code
+COPY . .
+
+# Build the server binary
+RUN go build -o app ./cmd/server
+
+# Final lightweight stage
+FROM alpine:latest
+
+# Install CA certificates for HTTPS
+RUN apk --no-cache add ca-certificates
+
+# Set working directory
+WORKDIR /root/
+
+# Copy binary from builder stage
+COPY --from=builder /app/app .
+
+# Expose port 8080
+EXPOSE 8080
+
+# Start the server
+CMD ["./app"]