send Kodi's watched history from a settings button

Not automatically on the service's first start any more: with several Kodi
installs, only the one whose history counts should send it. The button
("Send this Kodi's watched history to the server") asks first, shows progress
and can be cancelled; sending again is harmless, the server keeps newer state.

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

resources/settings.xml

@@ -3,4 +3,7 @@
     <!-- the server, e.g. https://media.example.com ("api_url" for older versions' value, which ended with /api) -->
     <setting id="api_url" type="text" default="" label="Server URL"/>
     <setting id="auth_key" type="text" default="" label="Auth key"/>
+    <!-- on the Kodi whose watched history counts (e.g. the main one); the server keeps what's newer -->
+    <setting id="send_history" type="action" label="Send this Kodi's watched history to the server"
+             action="RunPlugin(plugin://plugin.video.sklk/?action=send_history)"/>
 </settings>