Fix local folder playback after app container UUID changes

After iOS reinstall/restore the app container UUID rotates, which left both
the persisted source.url and the security-scoped bookmark pointing at a
no-longer-current path. Files derived a stale absolute path that got appended
onto the resolved bookmark, producing doubled URLs that MPV could not load.

- Resolve the base URL by picking whichever of the bookmark or source.url
  actually exists on disk.
- Compute MediaFile relative paths against the resolved root so they survive
  later container changes.
- Hold the security-scoped resource access for the source's lifetime via a
  shared resolver, so MPV can open files long after the directory enumeration
  that resolved the bookmark has returned.
- Normalize legacy absolute paths embedded in old recents/history video IDs
  so they re-resolve under the current container.

Yattee/Services/Player/PlayerService.swift

@@ -1394,8 +1394,20 @@ final class PlayerService {
         LoggingService.shared.debug("[SubtitleDebug] Found source: \(source.name), type: \(source.type)", category: .player)
 
         let password = mediaSourcesManager?.password(for: source)
-        let parentPath = (filePath as NSString).deletingLastPathComponent
-        let fileName = (filePath as NSString).lastPathComponent
+
+        // Legacy video IDs for `.localFolder` sources may carry an absolute container
+        // path (recorded before relative paths were computed correctly). Normalize
+        // against the source folder name so the path becomes relative and doesn't
+        // get appended onto the freshly resolved bookmark base, which would produce
+        // a doubled `/Documents/<folder>/private/var/.../Documents/<folder>/...` path.
+        let normalizedFilePath: String
+        if source.type == .localFolder {
+            normalizedFilePath = LocalFileClient.normalizeAbsolutePath(filePath, sourceFolderName: source.url.lastPathComponent)
+        } else {
+            normalizedFilePath = filePath
+        }
+        let parentPath = (normalizedFilePath as NSString).deletingLastPathComponent
+        let fileName = (normalizedFilePath as NSString).lastPathComponent
 
         LoggingService.shared.debug("[SubtitleDebug] parentPath: \(parentPath), fileName: \(fileName)", category: .player)