Schedule metadata reconciliation page jobs

[chubes4]

Summary

• Adds reconcile-metadata --apply --via-jobs --limit=N support for scheduling bounded metadata reconciliation pages.
• Reuses existing cleanup chunk task plumbing while executing page jobs through the direct apply path.
• Records scheduled offsets, job ids, pagination, summary, and elapsed timing evidence.

Closes #342.

Stacking

• Stacked on Support bounded metadata reconciliation apply #345 (fix/343-direct-reconcile-apply) because page jobs use direct bounded apply.

Testing

• php tests/smoke-worktree-metadata-reconcile.php
• php tests/smoke-worktree-cleanup-chunks.php
• php -l on changed PHP files
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted and implemented job-backed reconciliation scheduling and smoke coverage; Chris retains review and merge responsibility.