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/Services/Navigation/URLRouter.swift

@@ -12,6 +12,18 @@ struct URLRouter: Sendable {
 
     // MARK: - Main Routing
 
+    /// Route a URL only if we are *confident* the app can handle it natively —
+    /// YouTube/PeerTube video/channel/playlist, direct media (mp4/m3u8/etc),
+    /// or the custom `yattee://` scheme. Unlike `route(_:)` this deliberately
+    /// skips the `.externalVideo` yt-dlp fallback, which matches almost any
+    /// http/https URL and is therefore unsafe to trigger blindly after
+    /// resolving a URL shortener.
+    func routeConfidently(_ url: URL) -> NavigationDestination? {
+        guard let destination = route(url) else { return nil }
+        if case .externalVideo = destination { return nil }
+        return destination
+    }
+
     /// Route a URL to a navigation destination.
     func route(_ url: URL) -> NavigationDestination? {
         // Try custom scheme first