Promote Unreleased to v1.6.0

Ships Phase 5 (portable users get update notifications via BrowserNotifyUpdateService) to real users. This is the first release where the v1.5.0 Setup-installed users will get the auto-update banner (no prior Velopack release existed at v1.5.0 tag time), and the first release where v1.5.0+ portable users will see the in-app notification pointing them at the new release.

Minor bump rather than patch because portable-user update notifications are a meaningful user-facing capability addition.

AI-Local-Session: 4519f6b6-393a-4476-8efa-410e5396c3a9

AI-Cloud-Session: 72f9e474-60ab-42c2-b2a0-28fee827cbbb

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Geeven Singh

CHANGELOG.md

@@ -12,6 +12,8 @@ body. Keep section headings exact and write notes in Markdown.
 
 ## [Unreleased]
 
+## [1.6.0] - 2026-05-31
+
 ### Added
 
 - **Portable users now get update notifications too.** Previously the