feat: instant UI update after manual track mapping

- Backend now returns mapped track details after saving
- Frontend updates track in-place without requiring page refresh
- Track status changes from External to Local immediately
- Map button is removed after successful mapping
- Playlist counts refresh in background
- Improved UX: no more 'refresh the playlist' message

All 225 tests pass.

allstarr/Controllers/AdminController.cs

@@ -656,6 +656,37 @@ public class AdminController : ControllerBase
             
             _logger.LogInformation("Cleared playlist caches for {Playlist} to force rebuild", decodedName);
             
+            // Fetch the mapped Jellyfin track details to return to the UI
+            try
+            {
+                var trackUrl = $"{_jellyfinSettings.Url}/Items/{request.JellyfinId}?api_key={_jellyfinSettings.ApiKey}";
+                var response = await _jellyfinHttpClient.GetAsync(trackUrl);
+                
+                if (response.IsSuccessStatusCode)
+                {
+                    var trackData = await response.Content.ReadAsStringAsync();
+                    using var doc = JsonDocument.Parse(trackData);
+                    var track = doc.RootElement;
+                    
+                    var mappedTrack = new
+                    {
+                        id = request.JellyfinId,
+                        title = track.TryGetProperty("Name", out var nameEl) ? nameEl.GetString() : "",
+                        artist = track.TryGetProperty("AlbumArtist", out var artistEl) ? artistEl.GetString() : 
+                                 (track.TryGetProperty("Artists", out var artistsEl) && artistsEl.GetArrayLength() > 0 
+                                  ? artistsEl[0].GetString() : ""),
+                        album = track.TryGetProperty("Album", out var albumEl) ? albumEl.GetString() : "",
+                        isLocal = true
+                    };
+                    
+                    return Ok(new { message = "Mapping saved successfully", track = mappedTrack });
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to fetch mapped track details, but mapping was saved");
+            }
+            
             return Ok(new { message = "Mapping saved successfully" });
         }
         catch (Exception ex)