tables/detect_rects: prefer rect-grid edges over text-cluster on N≥3 column tables (#82)

When a wire-bordered table has headers centered/right-aligned in their
cells but data left-aligned, cluster_x_positions can both merge adjacent
data columns (when the data-to-data gap is below the clamped threshold)
and drop the header-only x-positions in its singleton-filter pass. The
cell-rect fallback then used text-cluster column edges and lost a column
or fragmented neighbor cells.

Prefer rect-derived column edges when the rect grid has 3+ columns and
every rect column holds multiple text items. The all-cols-populated
check protects against decorative or background rects (prose laid out
in a frame, cell-fill rects with extra borders) that would otherwise
split a logical column into spurious sub-columns. The existing
prose-in-frame, well-distributed-columns, and wireless-prose guards
still fire for the cases they were built for.

Bump napi version 1.8.7 → 1.8.8.

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

napi/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@firecrawl/pdf-inspector",
-  "version": "1.8.7",
+  "version": "1.8.8",
   "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",