Restructure project layout and add ECR repository CloudFormation template

- Move application entrypoint to cmd/lambda/
- Move Dockerfile to docker/ for clearer build context separation
- Promote go.mod/go.sum to project root
- Move CloudFormation templates under infra/cfn/ for consistent infra layout
- Add new template-container-repository.yaml defining ECR repository (blog-deployment)
- Move Lambda test files to test/ directory

docker/Dockerfile

@@ -0,0 +1,17 @@
+FROM docker.io/golang:1.24.2-bookworm as build
+WORKDIR /app
+# Copy dependencies list
+COPY ./app/go.mod ./
+COPY ./app/go.sum ./
+# Build with optional lambda.norpc tag
+COPY ./app/main.go ./
+RUN go build -tags lambda.norpc -o main main.go
+# Copy artifacts to a clean image
+FROM public.ecr.aws/lambda/provided:al2023
+# Install git and zip using dnf (Amazon Linux 2023)
+RUN dnf update -y && \
+    dnf install -y git zip && \
+    dnf clean all
+COPY --from=build /app/main ${LAMBDA_TASK_ROOT}
+WORKDIR ${LAMBDA_TASK_ROOT}
+ENTRYPOINT [ "./main" ]