fix(ralph): require rerunnable completion evidence

[jorgecurious]

Summary

• add a Ralph completion gate that requires monitor-rerunnable final verification evidence before <promise>COMPLETE</promise>
• extend the default task template and skill docs with final verification/artifact preservation fields
• queue Ralph follow-up messages with streamingBehavior: "followUp" to avoid runtime warnings while the agent is still processing

Verification

• installed the local pi-ralph-wiggum package via pi install ./pi-ralph-wiggum
• ran pi -p "Use Ralph Wiggum if available to report status only, then stop. Do not start a loop."
• ran git diff --check