test(printplay): #204 extract recto-verso back reorder to pure method + 9 tests - #500

…tests (#512)

The Print & Play PDF (PrintAndPlayDocument) computed four derived layout
quantities inline in Compose() with ZERO unit coverage: nbColumns,
nbRows, nbCardsPerPage, nbPages. A regression in any of them (rounding
instead of truncating columns, forgetting the header reserve, flooring
instead of ceiling the page count) silently changes how many sheets
print and how cards distribute across them, caught only by rendering and
eyeballing the PDF.

Extracts the arithmetic output-neutral into a pure, deterministic
ComputePageGeometry (no QuestPDF dependency, no I/O) + a
PrintPlayPageGeometry readonly struct. The call site preserves the exact
computation (verified by reading the old inline block before extraction),
so rendered output is byte-for-byte unchanged.

13 contract tests pin the layout contract additively (mirrors #500's
recto-verso reorder test conventions):
- columns: configured honored when >0; zero/negative fall back to floor
  division; floor-TRUNCATION not rounding (the fragile bit)
- rows: floor division of content height
- cardsPerPage = rows x columns
- pages: ceil(count/perPage); partial last sheet still prints; exact
  multiple; zero cards -> zero pages
- header reserves pageHeight/10 (matches ComposePage header band)
- margin subtracted from both dimensions

Gate-safe: additive tests + output-neutral extraction. The latent
divide-by-zero when cardsPerPage==0 (card larger than content area) is
preserved as-is, NOT guarded, and flagged in the XML doc for a separate
behavior-change PR.

Suite: 342 passed / 0 failed / 5 skipped (baseline 329 + 13 new).

Contributes to #204. Refs #500 (sibling recto-verso extraction).

Co-authored-by: Your <your.email@example.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

… method + 9 tests (#521)

PdfManager.GenerateAlternateFaceAndBack (the #119 contract) assembles a single
PDF where each card's BACK is emitted immediately before its FRONT so that on a
recto-verso sheet each back lines up behind its matching front, and the ORIGINAL
CardSet order is preserved (so back-less Rules keep their place and appear first).
This ordering is a fragile contract with ZERO unit coverage — a regression
emitting front-then-back, dropping the back-less cards, or reordering by
back-presence silently misaligns every printed sheet, caught only by printing.

Extracts the path-sequencing output-neutral into a pure, deterministic
OrderImagesForAlternateFaceAndBack (static, no MagickImage, no I/O). The call
site emits the exact same path sequence (verified by reading the old inline
builder before extraction), so rendered output is byte-for-byte unchanged.

9 contract tests pin the contract additively (mirror #500 recto-verso reorder +
#512 page-grid geometry conventions):
- per-card: back-then-front when a back exists; front-only when no back;
  empty back == no back (the IsNullOrEmpty guard)
- ordering: original CardSet order preserved (mixed backs NOT grouped); a
  back-less head card stays first (the Rules-first #119 guarantee)
- counts: all-with-back doubles the slot count; all-without-back singles
- pairing: back immediately precedes its OWN front (indices 2i, 2i+1)
- degenerate: empty input emits nothing

Gate-safe: additive tests + output-neutral extraction. Suite 351/0/5
(baseline 342 + 9 new).

Contributes to #204. Refs #500/#512 (sibling recto-verso extractions), #119.

Co-authored-by: Your <your.email@example.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>