Add delete button for manual track mappings

- Added DELETE /api/admin/mappings/tracks endpoint
- Removes mapping from JSON file and Redis cache
- Deletes file if it becomes empty after removal
- Added 'Remove' button to each mapping in web UI
- Enhanced confirm dialog explaining consequences for both local and external mappings
- Supports removing both Jellyfin (local) and external provider mappings
- Allows phasing out local mappings in favor of Spotify Import plugin

allstarr/Controllers/AdminController.cs

@@ -2957,6 +2957,66 @@ public class AdminController : ControllerBase
         }
     }
     
+    /// <summary>
+    /// Delete a manual track mapping
+    /// </summary>
+    [HttpDelete("mappings/tracks")]
+    public async Task<IActionResult> DeleteTrackMapping([FromQuery] string playlist, [FromQuery] string spotifyId)
+    {
+        if (string.IsNullOrEmpty(playlist) || string.IsNullOrEmpty(spotifyId))
+        {
+            return BadRequest(new { error = "playlist and spotifyId parameters are required" });
+        }
+        
+        try
+        {
+            var mappingsDir = "/app/cache/mappings";
+            var safeName = string.Join("_", playlist.Split(Path.GetInvalidFileNameChars()));
+            var filePath = Path.Combine(mappingsDir, $"{safeName}_mappings.json");
+            
+            if (!System.IO.File.Exists(filePath))
+            {
+                return NotFound(new { error = "Mapping file not found for playlist" });
+            }
+            
+            // Load existing mappings
+            var json = await System.IO.File.ReadAllTextAsync(filePath);
+            var mappings = JsonSerializer.Deserialize<Dictionary<string, ManualMappingEntry>>(json);
+            
+            if (mappings == null || !mappings.ContainsKey(spotifyId))
+            {
+                return NotFound(new { error = "Mapping not found" });
+            }
+            
+            // Remove the mapping
+            mappings.Remove(spotifyId);
+            
+            // Save back to file (or delete file if empty)
+            if (mappings.Count == 0)
+            {
+                System.IO.File.Delete(filePath);
+                _logger.LogInformation("🗑️ Deleted empty mapping file for playlist {Playlist}", playlist);
+            }
+            else
+            {
+                var updatedJson = JsonSerializer.Serialize(mappings, new JsonSerializerOptions { WriteIndented = true });
+                await System.IO.File.WriteAllTextAsync(filePath, updatedJson);
+                _logger.LogInformation("🗑️ Deleted mapping: {Playlist} - {SpotifyId}", playlist, spotifyId);
+            }
+            
+            // Also remove from Redis cache
+            var cacheKey = $"manual:mapping:{playlist}:{spotifyId}";
+            await _cache.DeleteAsync(cacheKey);
+            
+            return Ok(new { success = true, message = "Mapping deleted successfully" });
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to delete track mapping for {Playlist} - {SpotifyId}", playlist, spotifyId);
+            return StatusCode(500, new { error = "Failed to delete track mapping" });
+        }
+    }
+    
     /// <summary>
     /// Test Spotify lyrics API by fetching lyrics for a specific Spotify track ID
     /// Example: GET /api/admin/lyrics/spotify/test?trackId=3yII7UwgLF6K5zW3xad3MP