update: align template memory checkpoint with fallback policy

[Pedrohgv]

Summary

• Update templates/agent-state-template/cron/jobs.json to position the memory checkpoint as a fallback mechanism.
• Keep the template cron behavior aligned with the state-repo policy: write-at-source is primary, checkpoint only fills real gaps.
• Preserve idempotent updates to memory/flush-state.json while avoiding unnecessary rewrites.