fix: increase edge line count to catch form column headers as repeated content

Bumps EDGE_LINE_COUNT from 3 to 4 to strip repeated form column headers
that sit just inside the page margin (4th-from-edge Y position).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/markdown/preprocess.rs

@@ -214,8 +214,9 @@ pub(crate) fn strip_repeated_lines(lines: Vec<TextLine>, page_count: u32) -> Vec
     // A line is in the page margin if it's among the first or last N distinct
     // Y positions on that page. This is more robust than a percentage-based zone
     // because it catches actual edge lines regardless of how much content fills
-    // the page. N=3 accommodates multi-line headers/footers (e.g., nav bar + title).
-    const EDGE_LINE_COUNT: usize = 3;
+    // the page. N=4 accommodates multi-line headers/footers and repeated form
+    // column headers that sit just inside the page margin.
+    const EDGE_LINE_COUNT: usize = 4;
 
     /// Returns true if the line is among the first or last N distinct Y positions
     /// on its page.

tests/snapshots/p1244-1996.md

@@ -33,19 +33,19 @@ Date Date **a. Tips received**
 **b. Credit card tips c. Tips paid out to d. Names of employees to whom you**
 tips of directly from customers received other employees paid tips rec’d. entry and other employees 1 2 3 4 5 **Subtotals** **For Paperwork Reduction Act Notice, see Instructions on the back of Form 4070. Page 1**
 
-received other employees paid tips rec’d. entry and other employees
+rec’d. entry and other employees
 
 7 8 9 10 11 12 13 14 15 **Subtotals**
 
 **Page 2**
 
-received other employees paid tips rec’d. entry and other employees
+rec’d. entry and other employees
 
 17 18 19 20 21 22 23 24 25 **Subtotals**
 
 **Page 3**
 
-received other employees paid tips rec’d. entry and other employees
+rec’d. entry and other employees
 
 27 28 29 30 31 **Subtotals** **from pages** **1, 2, and 3** **Totals**