Resolve URL shorteners and prompt for ambiguous description links

Tapping bit.ly/tinyurl/t.co/etc. in a description or comment previously
opened Safari even when the destination was a playable YouTube URL.
Added an opt-in "Resolve Short Links" toggle under YouTube Enhancements
(off by default) that follows the redirect on tap: if the target is a
YouTube/PeerTube/direct-media URL, open it in-app; otherwise prompt the
user before falling back to yt-dlp extraction or the browser.

Also added a confirmation dialog for non-shortener links that only
matched the loose .externalVideo yt-dlp fallback, so arbitrary web
pages in descriptions no longer silently kick off extraction.

Prompts live on NavigationCoordinator and are dual-hosted by YatteeApp
and ExpandedPlayerSheet so they remain visible whether or not the
expanded player is covering the main view.

Yattee/Core/SettingsManager.swift

@@ -54,6 +54,9 @@ final class SettingsManager {
     var _deArrowAPIURL: String?
     var _deArrowThumbnailAPIURL: String?
 
+    // Short link resolution
+    var _resolveShortLinksEnabled: Bool?
+
     // User Agent
     var _customUserAgent: String?
     var _randomizeUserAgentPerRequest: Bool?
@@ -419,6 +422,7 @@ final class SettingsManager {
         _deArrowReplaceThumbnails = nil
         _deArrowAPIURL = nil
         _deArrowThumbnailAPIURL = nil
+        _resolveShortLinksEnabled = nil
         _customUserAgent = nil
         _randomizeUserAgentPerRequest = nil
         _feedCacheValidityMinutes = nil