sync watched state with the server, single server url setting

- list items take playcount, resume point and last played from the server
  (folders: watched/total episodes), listings aren't cached
- background service (service.py) reports playback to <server>/api/state/<id>:
  every 30 s, on pause, stop and end; on first start it sends Kodi's existing
  watched history of this add-on to the server once
- one "Server URL" setting instead of api + video url (the old api url value,
  ending with /api, still works); no default address

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

addon.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <addon id="plugin.video.sklk"
-       version="0.0.23"
+       version="0.0.24"
        name="sklk"
        provider-name="krk">
     <requires>
@@ -10,6 +10,8 @@
     <extension point="xbmc.python.pluginsource" library="main.py">
         <provides>video</provides>
     </extension>
+    <!-- reports playback to the server, which keeps watched state for all apps -->
+    <extension point="xbmc.service" library="service.py" start="login"/>
     <extension point="xbmc.addon.metadata">
         <summary lang="en">sklk pluginas</summary>
         <description lang="en_GB">nera jokio aprasymo</description>
@@ -18,6 +20,6 @@
             <icon>icon.png</icon>
             <fanart>fanart.jpg</fanart>
         </assets>
-        <news>jokiu naujienu..</news>
+        <news>0.0.24: watched state and resume points kept on the server, shared with other apps</news>
     </extension>
 </addon>