Release 0.2.0-rc.1

The first release candidate of 0.2.0: DNSSEC signing and Porkbun
support, two-factor login, view colours and navigation, and the build
shown in a footer. Its notes are the CHANGELOG's Unreleased section.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/install.md

@@ -387,9 +387,12 @@ sudo apt update && sudo apt upgrade      # Debian packages from the registry
 make && sudo make install && sudo systemctl restart jarl   # make install
 ```
 
-Database migrations run automatically at startup. Before an upgrade, take
-a backup (it is safe while jarld runs); `jarld restore` puts it back if
-needed:
+Database migrations run automatically at startup. An older Jarl refuses
+to start on a database a newer one has upgraded ("database schema version
+4 is newer than this Jarl"). So going back to an earlier version, after
+trying a release candidate say, means restoring a backup taken before the
+upgrade. Before an upgrade, take a backup (it is safe while jarld runs);
+`jarld restore` puts it back if needed:
 
 ```sh
 sudo jarld backup