fix(math): add MathRun to sliceRunsForLine so math renders in DomPainter

MathRun was silently dropped by sliceRunsForLine because it has no
`text` property. The `if (!('text' in run)) continue` guard filtered
it out before it could reach the renderer. Added an explicit
`run.kind === 'math'` case matching the existing image/tab/fieldAnnotation
pattern.

SD-2369

Author: caio-pizzol

packages/layout-engine/painters/dom/src/renderer.ts

@@ -7490,6 +7490,12 @@ export const sliceRunsForLine = (block: ParagraphBlock, line: Line): Run[] => {
       continue;
     }
 
+    // MathRun handling - math runs are atomic units like images
+    if (run.kind === 'math') {
+      result.push(run);
+      continue;
+    }
+
     // At this point, run must be TextRun (has .text property)
     if (!('text' in run)) {
       continue;