Add URL scheme actions: play, queue, download, bookmark, subscribe, player controls

yattee://play|play-next|queue|download|bookmark|subscribe|unsubscribe?url={link}
and yattee://player/play|pause|toggle|next|previous|close|seek|rate run through
one LinkActionPerformer that reports a LinkActionResult, ready for
x-callback-url. An unencoded url= keeps its own query; only the action's own
parameters end it.

Actions that change saved state ask first through a confirmation sheet
presented by the top-most sheet host, unless the new 'Run Link Actions
Without Asking' setting is on. Download skips the question when the quality
picker will show anyway. Player commands leave sheets and the player alone.

Yattee/Services/Navigation/URLRouter.swift

@@ -301,6 +301,8 @@ struct URLRouter: Sendable {
             return nil
 
         default:
+            // Action hosts (yattee://play, yattee://player/…) are LinkActionParser's
+            if LinkActionParser.hosts.contains(host) { return nil }
             return parseLegacyScheme(url)
         }
     }