Stage 1 exclusive item-to-cell assignment, v1.6.4 (#66)

Closes the row-merge pattern observed against FNBO branch list at the
College/Fairway boundary: when SLANet emits cells whose y-extents
overlap between consecutive rows, an item whose center fell in the
overlap region got pulled into BOTH cells, producing run-on cells
(e.g. "Kansas Kansas" + concatenated addresses).

Cause: stage 1's "for each cell, gather items inside" loop allowed an
item to match multiple cells. `normalize_cell_bands` reduces overlap
but is biased when cell-mean-center is offset from actual text baseline
(SLANet bboxes are typically taller than their text content), so the
midpoint-clamp can land on the wrong side of the row boundary, and
items at the boundary still match two cells.

Fix: invert the matching. For each PDF text item, find candidate cells
(those whose bbox satisfies tsr_region_contains_item — center inside
OR >=60% overlap on both axes), and assign to the cell whose CENTER
is geometrically closest. Build per-cell text from the assigned items.
Stage 2 (orphan recovery) is unchanged.

Exclusivity prevents item duplication across cells. The closest-center
rule disambiguates the cell-overlap case naturally without aggressive
band clamping. normalize_cell_bands stays — it tightens cells before
matching (smaller overlap → fewer ambiguous candidates) but is no
longer load-bearing for correctness of the overlap case.

Local replay against FNBO via api/scripts/local-tsr-replay.ts (which
exercises the full layout-pod → table-pod → pdf-inspector chain
in-process):

  Pre-1.6.4 (deployed 1.6.3):
    |LITH West|Illinois Illinois|11700 S. IL Route 47, Huntley IL...
    |College|||0534.03|
    |Fairway|Kansas Kansas|4650 College Blvd... 2828 Shawnee Mission...

  Post-1.6.4 (this change):
    |Huntley|Illinois|11700 S. IL Route 47, Huntley IL...|8711.15|
    |LITH West|Illinois|4520 W Algonquin Rd, Lake in the Hills...
    |College|Kansas|4650 College Blvd, Overland Park KS...|0532.01|
    |Fairway|Kansas|2828 Shawnee Mission Pkwy, Fairway KS...|0500.00|

One row (Shawnee in the Kansas section) can still get dropped under
SLANet detection variance — the model occasionally under-detects rows
and emits N structure rows for N+1 PDF rows. The squeezed row's text
gets routed to the structurally-nearest existing cell. This is a
SLANet limitation, not addressable in pdf-inspector without
synthesizing rows from PDF text geometry; deferred.

Tests: 416 lib + 120 integration + 2 doctests pass. clippy + fmt clean.

Bump @firecrawl/pdf-inspector to 1.6.4 (patch — refines stage 1's
matching strategy; no API changes).

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

napi/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@firecrawl/pdf-inspector",
-  "version": "1.6.3",
+  "version": "1.6.4",
   "description": "Fast PDF classification and text extraction. Detect text-based vs scanned PDFs, extract text by region with quality checks. Native Rust performance via napi-rs.",
   "main": "index.js",
   "types": "index.d.ts",