Fix published date handling in Piped API

Clear the published string when a proper publishedAt date is extracted from uploadDate to prevent duplicate or inconsistent date display. Only fallback to string-based published date when no structured date is available.

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

Model/Applications/PipedAPI.swift

@@ -556,7 +556,8 @@ final class PipedAPI: Service, ObservableObject, VideosAPI {
            let formattedDate = dateFormatter.date(from: date)
         {
             publishedAt = formattedDate
-        } else {
+            published = ""
+        } else if published.isNil {
             published = (details["uploadedDate"] ?? details["uploadDate"])?.string ?? ""
         }