feat(waveform): generalize high-res compute to every track (Direction B)

Per-track high-res datum keyed by EntryKey in the renamed track-waveforms vault; computed at upload for all tracks, regenerable per-track via CMS, with a re-runnable backfill. Mix read path repointed so it keeps working.

DeepDrftAPI/Controllers/ReleaseController.cs

@@ -68,7 +68,8 @@ public class ReleaseController : ControllerBase
 
     // GET api/release/{entryKey}/mix/waveform (unauthenticated)
     // Serves the high-res waveform datum for a Mix release as base64. Mirrors GET api/track/{id}/waveform
-    // but reads from the mix-waveforms vault. 404 when the release is not a Mix, carries no waveform key,
+    // but reads the Mix's track datum from the track-waveforms vault. 404 when the release is not a Mix,
+    // carries no waveform key,
     // or no datum is stored. Public read — addresses by the opaque EntryKey, not the int PK (§3e). The
     // {entryKey} string segment cannot collide with the ApiKey-gated POST {id:long}/mix/waveform (different
     // verb + constraint). Declared before the shorter "{entryKey}" route for clarity.
@@ -91,7 +92,7 @@ public class ReleaseController : ControllerBase
             return NotFound();
         }
 
-        var bytes = await _waveformProfileService.GetProfileAsync(waveformEntryKey, VaultConstants.MixWaveforms);
+        var bytes = await _waveformProfileService.GetProfileAsync(waveformEntryKey, VaultConstants.TrackWaveforms);
         if (bytes is null)
         {
             _logger.LogInformation("Mix waveform key set but no datum stored for release: {EntryKey}", entryKey);