v0.2.0 — Table fidelity

A sustained pass over how the pipeline handles textbook tables, driven by measuring the real
corpus rather than by intuition. Every change defaults to preserving prior output (a kill-switch
restores byte-identical behavior) unless it corrects output that was already wrong.

Added

• Cross-page table merge (T2N_TABLE_MERGE=1, default OFF) — stitch a table that ends near
  a page bottom to a geometrically-matching table at the top of the next page; dedupes the
  repeated header, leaves a <!-- table continues from page N --> trace.
• Docling table rung (T2N_DOCLING=1, default OFF) — a layout-model table extractor that
  gets multi-column shape right where pdfplumber collapses borderless grids; falls back to
  pdfplumber per-page when it finds nothing, so no page is left worse off.
• Table QC gate — flags structural damage (ragged rows, empty first cell, run-together
  text, single-column collapse, content-retention) with a <!-- ⚠️ … --> trace, never
  auto-"fixing" it.
• Out-of-band review queue (T2N_REVIEW_QUEUE=1, default OFF; recommended ON for clinical
  corpora) — the QC gate sees structure but not misbinding (a value merged into the wrong
  row of an otherwise clean grid). There is no safe automatic fix, so the high-risk subset
  (continuation-page tables + dosage/threshold tables) is flagged for a bring-your-own-model
  second opinion. In testing ~1 in 6 continuation×dose tables carried a high-severity misbinding
  vs ~0 in a random sample. See docs/table-review.md.
• Spanned category-header collapse (T2N_TABLE_HEADER_COLLAPSE=1, default ON) — a section
  header broadcast across every column of a wide grid becomes a phantom full-width data row. A
  real data row never repeats one ≥15-char string across ≥3 columns, so the row is re-cast as a
  single header cell — structural only, never moves a value between rows. Hit 130/232 (56%) of
  one dense pharmacology reference's tables.
• Book-level table-reliability banner (detection only) — when ≥40% of a book's tables (given
  ≥10) trip a QC flag, a > [!caution] banner is hung at the top of the markdown telling the
  downstream model to verify every table against the source PDF; reliability_flagged /
  flag_rate land in the per-book stats. One reference ran 66%.
• Whole-book table-failure warning (T2N_BOOK_TABLE_CHECK, default ON) — table loss is
  bimodal (a book extracts fine or loses every table); a loud warning is emitted when a book
  yields 0 tables despite ≥10 captions, or pdfplumber parses 0 pages while fitz opens fine.

Fixed

• Page-frame pseudo-table rejection (T2N_TABLE_FRAME_REJECT, default ON) — page-decoration
  rectangles made pdfplumber "find" a whole-page 1-column table that dumps every word into one
  cell (real multi-column tables arrive column-interleaved but caption-and-values intact, reading
  as clean data while the binding is destroyed). Rejected and replaced by a trace comment.
  Measured at 9.9% of extracted tables across 128 books.
• Two false-positive table detections — running prose and a navigation strip that the frame
  heuristic misread as tables, narrowed without regressing real rejections.
• Docling ligature corruption — repair ligature glyphs against the page's own text layer
  before emitting, so the markdown and the QC retention check both see corrected text.
• Furniture false-rejections — a geometry-only running-header/footer band rule, measured for
  its false-kill rate and narrowed.