[ilyaZar]

webui.remove-profile refused to run when any theme other than default or the
adapter's own was selected, such as Syncthing's Dark. Users hit an error for a
setting that has nothing to do with the plugin.

Only one case needs care: deleting an adapter's files while its own theme is
selected. So the rule is now:

• own theme selected: switch to default
• any other theme: leave it alone
• either way: delete only this adapter's folders

Also in this PR:

• shared success message no longer claims the default was restored
• Caelestia README no longer asks to apply Default first
• bundled binaries and checksums rebuilt

hosts/omarchy is unchanged: it has its own removal script.

Testing

• new TestProfileCleanupLeavesAThemeItDoesNotOwn, fails without the fix
• Go race and vet, integration, verify.sh, checksums, installation,
  architecture and device-sharing tests pass
• not run: tests/plugin-ui.test.sh; the only QML change is one message
• not tried on a real shell yet