v0.1.6: spreadsheet fidelity and evidence records

Preserve XLSX row/column coordinates, merged references, native values, formulas, formats, hidden state and annotations. Preserve stored values covered by merged cells separately and flag differences. Escape Markdown pipes and render cell line breaks. Recognize embedded raster images without resizing.

Add optional evidence=True / --evidence provenance JSON with hashes, converter/dependency versions and explicit coverage limits. Evidence mode distinguishes same-stem inputs and rejects changed sources. Staged publication prevents mismatched Markdown and manifests after write failures.

Validation: 31 tests pass with both supported OCR interfaces; a real workbook retains all 627 stored values and 69 merged ranges, including 24 values hidden by merges. These are conversion checks, not business audit or OCR accuracy certification. PDF table geometry and image entity counting remain outside this release.