fix: bound emergency cleanup task results

[chubes4]

Closes #980.

Summary

• Project recurring emergency-cleanup logs and completed job results to bounded operational evidence instead of persisting full candidate plans.
• Preserve trigger reasons, selected and scheduled counts/IDs, planned and measured recovery totals, action-required evidence, and compact capacity snapshots.
• Keep full reports unchanged for explicit workspace ability and CLI callers.

Verification

• php tests/workspace-disk-emergency-cleanup-durable-result.php
  • 4+ MiB fixture; log context: 970 bytes; completed result: 906 bytes; both enforced at <= 8,192 bytes.
• PHP lint passed for inc/Tasks/WorkspaceDiskEmergencyCleanupTask.php and tests/*.php.
• Full suite passed except two pre-existing standalone/environment failures: artifact-cleanup-live-process-guards.php requires Linux /proc process scanning, and worktree-cleanup-patch-equivalence.php lacks its GitCheckout bootstrap dependency.

AI Assistance

AI assistance disclosure: openai/gpt-5.6-sol using OpenCode implemented and tested the bounded result change. Chris remains responsible for every line.