docs: cut CHANGELOG 0.2.0, reopen Unreleased

Renames the Unreleased section to 0.2.0 per the versioning convention in
docs/progress.md — the accumulated panel/CI/ops work since 0.1.0 is a
coherent release (SemVer minor bump; project is still pre-1.0). No git
tag/image push yet; that stays an explicit step.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,8 +5,10 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ## [Unreleased]
 
+## [0.2.0] - 2026-08-03
+
 - panel: every authenticated page now ends with the running version
-  (`SelfPost 1.1.0`) in a small footer. It is the value a backup manifest is
+  (`SelfPost 0.2.0`) in a small footer. It is the value a backup manifest is
   checked against on restore, and the first thing to establish when the panel
   behaves unexpectedly. The login and setup pages deliberately do not show it.