ipx user rename: give an account the name the proxy signs it in as

An account made by hand before the proxy was set up is called what it was
given ('rays'), while Cloudflare Access vouches for an email address. With
auto_create_users on, the first visit through the tunnel would make a
second, empty account. Renaming keeps the id, so feeds, read state and
admin rights go with it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TAC7sLVqfKmY6rsTLXzNgk

CHANGELOG.md

@@ -14,6 +14,8 @@ The long form, with what was wrong before and how it was found, is in
 
 - Settings → Users and `ipx user list` show when each account was added and when it last signed
   in, to the hour.
+- `ipx user rename <name> <new name>` renames an account and keeps its feeds, read state and admin
+  rights. An account made before the proxy was set up can take the name the proxy signs it in as.
 
 ### Changed