Add CMS waveform pre-processing panel with backfill endpoints

GET api/track/waveform-status and POST api/track/{id}/waveform (ApiKey);
CmsTrackService methods; TrackPreProcessing page with per-row and
sequential bulk generation; nav links from TrackList and Index.

DeepDrftModels/DTOs/WaveformStatusDto.cs

@@ -0,0 +1,15 @@
+namespace DeepDrftModels.DTOs;
+
+/// <summary>
+/// Per-track waveform profile status for the CMS PreProcessing panel. Tells admins which tracks
+/// already carry a stored loudness profile and which predate the WaveformSeeker feature and need
+/// backfilling. <see cref="HasProfile"/> is the existence check; <see cref="EntryKey"/> is the
+/// vault key used to trigger generation for a missing profile.
+/// </summary>
+public class WaveformStatusDto
+{
+    public long TrackId { get; set; }
+    public string EntryKey { get; set; } = string.Empty;
+    public string TrackName { get; set; } = string.Empty;
+    public bool HasProfile { get; set; }
+}