Preserve ambiguous margin numbers in Markdown conversion

[silverstein]

Summary

Preserve competing bare-number labels in the same page margin band instead of treating them as pagination. Both default furniture removal and optional compact normalization use the same ambiguity protection. Ordinary isolated and labelled page numbers remain removable.

A fresh public-form diagnostic found four project-key labels removed near the bottom of an otherwise readable form. This fixes that content loss, not blank-grid reconstruction. Synthetic regressions cover headers, footers, repeated pages, compact/furniture combinations and a protected oversized label.

Renderer identity moves to 1.20.1 with matching source/share schemas and current-version gates. The generated layout oracle changes only the two module bindings and source-set digest; no occurrence answers changed. No package release version or binary artifact changes.

Verification

• Stonebook macOS arm64, Node v26.5.0, one Vitest worker.
• Focused renderer/conversion/map/bakeoff bank: 117 passed, 6 artifact-backed cases skipped.
• Output-schema and packager coverage: 29 passed.
• Verified-vision proposal packet: 9 passed.
• Original synthetic regressions failed on the base implementation; guarded paths pass.
• Read-only MCP replay of original public form retains all ten project-key labels; source PDF unchanged. Conversion remains honestly partial for unsupported grid structure.
• Source/share parity and diff checks pass.
• Independent exact-commit review: PASS at 7115ade.

Not a full release qualification, packaged bakeoff, desktop reinstallation, comparative benchmark or performance-superiority claim.