Update changelog for v0.6.6

Author: yeasy

CHANGELOG.md

@@ -8,6 +8,14 @@ All notable changes to this project will be documented in this file. The format
 
 ---
 
+## [0.6.6] - 2026-03-27
+
+### Fixed
+
+- **Duplicate chapter title in PDF**: Sub-chapters using h2–h6 in Markdown had their heading duplicated because the deduplication logic only matched h1 tags; now matches any heading level
+
+---
+
 ## [0.6.5] - 2026-03-27
 
 ### Security

cmd/root.go

@@ -13,7 +13,7 @@ import (
 
 var (
 	// Version is overridden at build time via -ldflags.
-	Version = "0.6.5"
+	Version = "0.6.6"
 	// BuildTime is overridden at build time via -ldflags.
 	BuildTime = "unknown"
 	// rootCmd is the root command for the mdpress application.