Add PIR remediation verification fixtures

[jddark62]

Summary

• Adds remediation verification inputs, closure criteria, verification methods, residual-risk status, and recurrence tracking to post-incident-review.
• Extends the remediation plan and output template with a verification register and recurrence table.
• Adds seven YAML edge-case fixtures covering premature ticket closure, detection replay, segmentation validation, vendor blockers, accepted risk, restore drills, recurrence reopen thresholds, and tabletop-required process updates.

Validation

• git diff --check
• Frontmatter YAML parse passed
• Fixture YAML parse passed: 7 blocks
• Markdown fence balance passed
• Required remediation verification and recurrence markers present
• ASCII scan passed for new fixture file
• Privacy scan passed for public files

/claim #897

Payment details can be coordinated privately after maintainer acceptance.