feat: add standalone rds-refresh component

Add a fully standalone version of the RDS/Aurora refresh tool that can
be built and deployed immediately without requiring a DBLab Engine
release. This version has no dependencies on DBLab internal packages.

The standalone component includes:
- Self-contained Go module with minimal dependencies
- Makefile for easy building (CLI, Lambda, Docker)
- SAM template for AWS Lambda deployment
- Dockerfile for container builds
- Comprehensive documentation

Can be used immediately by:
1. go build -o rds-refresh .
2. ./rds-refresh -config config.yaml

Author: claude

rds-refresh/Dockerfile

@@ -0,0 +1,39 @@
+# Build stage
+FROM golang:1.21-alpine AS builder
+
+RUN apk add --no-cache git ca-certificates
+
+WORKDIR /build
+
+# Copy go mod files first for better caching
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source code
+COPY *.go ./
+
+# Build the binary
+ARG VERSION=dev
+ARG BUILD_TIME=unknown
+
+RUN CGO_ENABLED=0 GOOS=linux go build \
+    -ldflags="-s -w -X main.version=${VERSION} -X main.buildTime=${BUILD_TIME}" \
+    -o /rds-refresh \
+    .
+
+# Runtime stage
+FROM alpine:3.19
+
+RUN apk add --no-cache ca-certificates tzdata
+
+# Create non-root user
+RUN adduser -D -u 1000 appuser
+
+WORKDIR /app
+
+COPY --from=builder /rds-refresh /usr/local/bin/rds-refresh
+
+USER appuser
+
+ENTRYPOINT ["/usr/local/bin/rds-refresh"]
+CMD ["--help"]

rds-refresh/Makefile

@@ -0,0 +1,49 @@
+.PHONY: build build-linux build-lambda clean test fmt vet
+
+VERSION ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
+BUILD_TIME ?= $(shell date -u +"%Y-%m-%dT%H:%M:%SZ")
+LDFLAGS = -ldflags "-s -w -X main.version=$(VERSION) -X main.buildTime=$(BUILD_TIME)"
+
+# Build for current platform
+build:
+	go build $(LDFLAGS) -o rds-refresh .
+
+# Build for Linux (for Docker/Lambda)
+build-linux:
+	GOOS=linux GOARCH=amd64 go build $(LDFLAGS) -o rds-refresh-linux-amd64 .
+	GOOS=linux GOARCH=arm64 go build $(LDFLAGS) -o rds-refresh-linux-arm64 .
+
+# Build Lambda bootstrap binary
+build-lambda:
+	GOOS=linux GOARCH=arm64 CGO_ENABLED=0 go build $(LDFLAGS) -o bootstrap .
+	zip rds-refresh-lambda.zip bootstrap
+	rm bootstrap
+
+# Clean build artifacts
+clean:
+	rm -f rds-refresh rds-refresh-linux-* bootstrap rds-refresh-lambda.zip
+
+# Run tests
+test:
+	go test -v ./...
+
+# Format code
+fmt:
+	go fmt ./...
+
+# Run go vet
+vet:
+	go vet ./...
+
+# Download dependencies
+deps:
+	go mod download
+	go mod tidy
+
+# Run locally (requires config.yaml)
+run:
+	go run . -config config.yaml
+
+# Run dry-run locally
+dry-run:
+	go run . -config config.yaml -dry-run