Label local-file video quality from mpv track info instead of Unknown

Streams built for local folder files carry no resolution/codec/fps
metadata (unknowable before demux), so the quality selector labeled
them "Unknown". Use the video track mpv reports (demux-w/h/fps, codec)
to fill those fields into a display-only copy of the stream — the
Video row and summary now show e.g. "720p · 30fps" with a codec badge.
Selection and tap handling keep using the original stream.

YatteeTests/MPVTrackTests.swift

@@ -42,6 +42,9 @@ struct MPVTrackDecodingTests {
         #expect(video.trackID == 1)
         #expect(video.isDefault)
         #expect(video.isSelected)
+        #expect(video.width == 3840)
+        #expect(video.height == 1600)
+        #expect(video.fps == 23.976)
 
         let mainAudio = tracks[1]
         #expect(mainAudio.type == .audio)