feat: force page break after heading blocks for clean chapter layout

src/reader.rs

@@ -180,6 +180,12 @@ pub fn recalculate_pages(
             } else {
                 current_height += needed;
             }
+
+            if block.heading_level >= 1 && i + 1 < section.blocks.len() {
+                page_block_ranges.push((page_start_block, i + 1));
+                page_start_block = i + 1;
+                current_height = 0.0;
+            }
         }
 
         if page_start_block < section.blocks.len() {