Stop tracking resume progress for live streams

With "Partially Watched Videos" set to Ask, opening a live stream showed
the resume sheet with a playback timestamp. A live position is relative
to the live edge, not a fixed timeline, so it is meaningless as a
playhead.

Live views are still recorded in history, but carry no resume position:

- WatchEntry gains a persisted isLive flag plus recordLiveWatch(), which
  stores no position and clears state a drifting HLS duration may have
  left behind. progress is always 0 and toVideo() propagates the flag so
  history rows render the LIVE badge.
- from(video:) clamps duration, keeping Piped's -1 live sentinel out of
  storage.
- DataManager routes live saves through recordLiveWatch() and clears the
  flag on the non-live path (before updateProgress, so the auto-finish
  check is not suppressed by the hard-0 live progress), letting an entry
  heal once the stream becomes a VOD.
- PlayerService skips completion saves, always starts at the live edge,
  and drops any startTime passed for a live video.
- The resume prompt, the "Continue at" button label, thumbnail progress
  bars, "X remaining", Continue Watching and tvOS Top Shelf all exclude
  live entries.
- CloudKit syncs isLive with the rest of the watch state: the conflict
  resolver carries it with watchedSeconds/isFinished and the sync engine
  applies it when merging into an existing entry. It is read leniently,
  so the schema version stays at 2 and older clients keep parsing these
  records.

Yattee/Views/Video/VideoInfoView.swift

@@ -232,6 +232,7 @@ struct VideoInfoView: View {
     /// and resume setting is continueWatching or ask.
     private var playButtonLabel: String {
         guard let video = displayedVideo,
+              !video.isLive,
               let savedProgress = dataManager?.watchProgress(for: video.id.videoID),
               savedProgress >= 5,
               video.duration > 0,
@@ -2269,7 +2270,14 @@ struct VideoInfoView: View {
     /// Play the video, respecting the user's resume action setting for partially watched videos.
     private func playVideo() {
         guard let video = displayedVideo, let env = appEnvironment else { return }
-        
+
+        // Live streams have no fixed timeline, so a resume position is meaningless -
+        // never ask, always join at the live edge.
+        guard !video.isLive else {
+            playVideoWithStartTime(0)
+            return
+        }
+
         // Get saved watch progress from database
         let savedProgress = env.dataManager.watchProgress(for: video.id.videoID)
         let videoDuration = video.duration