Switch dashboard to watcher-based multi-disk view, fix transcoding FPS display

- dashboard.html: remove standalone "Mounted Disk" input panel; show all disks
  from GET /api/disks (watcher), auto-refresh every 5s
- detect.go: use avg_frame_rate when r_frame_rate is unrealistic (>120 fps or 0),
  fixes MJPEG/mjpeg showing 90000fps
- transcoder.go: parse fps= from ffmpeg progress output and expose in Progress struct
- copier.go: update task message with real-time encoding fps (@ 45.3 fps),
  clear speed_bps/eta during transcoding to avoid showing stale copy speed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/copier/copier.go

@@ -393,23 +393,26 @@ func (c *Copier) processVideo(ctx context.Context, taskID string, database *db.D
 	ext := transcoder.OutputExt(profile.OutputFormat)
 	dstTranscoded := strings.TrimSuffix(dst, filepath.Ext(dst)) + ext
 
-	srcFPS := fmt.Sprintf("%.2f", info.FPS)
-	msg := fmt.Sprintf("Transcoding %s (%s/%dch/%sfps → %s/%s/%dfps %s)",
-		filepath.Base(src),
-		info.Codec, info.AudioChannels, srcFPS,
-		profile.VideoCodec, profile.AudioCodec, profile.MaxFPS, profile.OutputFormat,
-	)
+	srcInfo := fmt.Sprintf("%s/%dch/%.0ffps", info.Codec, info.AudioChannels, info.FPS)
+	dstInfo := fmt.Sprintf("%s/%s/%dfps %s", profile.VideoCodec, profile.AudioCodec, profile.MaxFPS, profile.OutputFormat)
+	baseMsg := fmt.Sprintf("Transcoding %s (%s → %s)", filepath.Base(src), srcInfo, dstInfo)
+
 	c.tasks.Update(taskID, func(t *task.Task) {
 		t.Phase = task.PhaseTranscoding
-		t.Message = msg
+		t.Message = baseMsg
 	})
 	if t, ok := c.tasks.Get(taskID); ok {
 		_ = database.UpdateTask(*t)
 	}
 
-	progressFn := func(pct float64) {
+	progressFn := func(p transcoder.Progress) {
 		c.tasks.Update(taskID, func(t *task.Task) {
-			t.Progress = int(pct * 100)
+			t.Progress = int(p.Pct * 100)
+			t.SpeedBPS = 0
+			t.ETASec = 0
+			if p.EncodeFPS > 0 {
+				t.Message = fmt.Sprintf("%s @ %.1f fps", baseMsg, p.EncodeFPS)
+			}
 		})
 	}