Migrate Entry Point to cmd/

[baync180705]

Move the main execution file to separate the binary from the library code. Tasks:

• Create directory cmd/sysreplicate.
• Move main.go → cmd/sysreplicate/main.go.
• Fix imports (paths relative to root need to be absolute github.com/mdgspace/sysreplicate/...).
• Acceptance Criteria: go run cmd/sysreplicate/main.go runs the tool successfully.