Promote [Unreleased] to [0.6.0] for release

User-facing changes since v0.5.0:
- New Diff dialog: ref picker on every commit-ish input + new
  Branch-vs-merge-base mode (#4)
- File-list filter + per-file Viewed checkbox, Hide-viewed toolbar
  toggle, Ctrl+/, Space (#3)

AI-Local-Session: 324bab9a-4598-4558-bfa8-945af6bc48db
AI-Cloud-Session: 620cead1-bd37-4511-a627-8793b66717fd
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: geevensingh

CHANGELOG.md

@@ -12,6 +12,8 @@ body. Keep section headings exact and write notes in Markdown.
 
 ## [Unreleased]
 
+## [0.6.0] - 2026-05-18
+
 ### Added
 
 - **New Diff dialog: ref picker for commit-ish inputs.** The
@@ -279,7 +281,8 @@ The binary is unsigned, so Windows SmartScreen may warn on first
 launch — click **"More info"** → **"Run anyway"**. Code signing is
 planned for a later release.
 
-[Unreleased]: https://github.com/geevensingh/DiffViewer/compare/v0.5.0...HEAD
+[Unreleased]: https://github.com/geevensingh/DiffViewer/compare/v0.6.0...HEAD
+[0.6.0]: https://github.com/geevensingh/DiffViewer/compare/v0.5.0...v0.6.0
 [0.5.0]: https://github.com/geevensingh/DiffViewer/compare/v0.4.0...v0.5.0
 [0.4.0]: https://github.com/geevensingh/DiffViewer/compare/v0.3.0...v0.4.0
 [0.3.0]: https://github.com/geevensingh/DiffViewer/compare/v0.2.0...v0.3.0