chore: restore pub(super) on placeholders and say title tiebreak

[seamus-sloan]

Summary

• Restore pub(super) on page::placeholders, per rule 05's visibility rule
• Fix the comment saying the offline replica breaks ties on id; it uses title

Test plan

• cargo nextest run -p omnibus-db books::page → 58 passed
• cargo fmt --check clean; clippy reports nothing in the touched files

Version

By default a merge to main cuts a patch release. Pick the version update this PR should trigger; labels override the default:

• Minor — add the minor version label (vX.Y.Z → vX.(Y+1).0).
• Patch — the default; add the patch version label or leave unlabeled (vX.Y.Z → vX.Y.(Z+1)).
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[github-actions]

cargo-audit

No RustSec advisories found in Cargo.lock ✅

_{Posted by the Rust workflow's security job.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

📢 Thoughts on this report? Let us know!

[Copilot]

🟢 Approval recommended

The documentation fixes are accurate, with only a nonblocking visibility-style concern.

1 open finding

• Avoid widening private helper visibility to pub(super) · New

What changed in this PR

Corrects offline-sort documentation and adjusts the SQL placeholder helper’s visibility.

Changes:

• Updates comments to name the title tiebreak correctly.
• Changes placeholders to pub(super).

File	Description
docs/​architecture.md	Corrects offline replica tiebreak documentation.
db/​src/​books/​projection.rs	Corrects the projection comment.
db/​src/​books/​page.rs	Changes helper visibility.

🧠 Review effort: Balanced

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