fix: render <br> between paragraphs as a visible section break (#2548)

Co-authored-by: Brooks Ilg <brooksmilg@gmail.com>

lib/Epub/Epub/blocks/BlockStyle.h

@@ -32,6 +32,11 @@ struct BlockStyle {
   bool isRtl = false;              // true if resolved direction is RTL
   bool directionDefined = false;   // true if direction was explicitly set in CSS/HTML
 
+  // Set when this block was created by a <br> element. Used by startNewTextBlock to inject
+  // a full line-height gap when the <br> block stays empty (section-break use case).
+  // NOT propagated through getCombinedBlockStyle so it can't leak into sibling blocks.
+  bool fromBrElement = false;
+
   // Combined insets (margin + padding)
   [[nodiscard]] int16_t leftInset() const { return marginLeft + paddingLeft; }
   [[nodiscard]] int16_t rightInset() const { return marginRight + paddingRight; }
@@ -92,6 +97,9 @@ struct BlockStyle {
       result.directionDefined = true;
     }
 
+    // fromBrElement is consumed by startNewTextBlock when an empty <br> block
+    // is merged with the following paragraph; never propagate it further.
+    result.fromBrElement = false;
     return result;
   }