feat: add Clear Cache & Rebuild button for playlists in Admin UI

- New endpoint: POST /api/admin/playlists/{name}/clear-cache
- Clears Redis cache keys (items, matched tracks, missing tracks)
- Deletes file caches
- Triggers automatic rebuild with latest code (includes Spotify IDs)
- Added prominent button in Admin UI playlist table
- Shows confirmation dialog with details of what will be cleared

allstarr/Controllers/AdminController.cs

@@ -935,6 +935,77 @@ public class AdminController : ControllerBase
         }
     }
     
+    /// <summary>
+    /// Clear cache and rebuild for a specific playlist
+    /// </summary>
+    [HttpPost("playlists/{name}/clear-cache")]
+    public async Task<IActionResult> ClearPlaylistCache(string name)
+    {
+        var decodedName = Uri.UnescapeDataString(name);
+        _logger.LogInformation("Clear cache & rebuild triggered for playlist: {Name}", decodedName);
+        
+        if (_matchingService == null)
+        {
+            return BadRequest(new { error = "Track matching service is not available" });
+        }
+        
+        try
+        {
+            // Clear all cache keys for this playlist
+            var cacheKeys = new[]
+            {
+                $"spotify:playlist:items:{decodedName}",      // Pre-built items cache
+                $"spotify:matched:ordered:{decodedName}",     // Ordered matched tracks
+                $"spotify:matched:{decodedName}",             // Legacy matched tracks
+                $"spotify:missing:{decodedName}"              // Missing tracks
+            };
+            
+            foreach (var key in cacheKeys)
+            {
+                await _cache.DeleteAsync(key);
+                _logger.LogDebug("Cleared cache key: {Key}", key);
+            }
+            
+            // Delete file caches
+            var safeName = string.Join("_", decodedName.Split(Path.GetInvalidFileNameChars()));
+            var filesToDelete = new[]
+            {
+                Path.Combine(CacheDirectory, $"{safeName}_items.json"),
+                Path.Combine(CacheDirectory, $"{safeName}_matched.json")
+            };
+            
+            foreach (var file in filesToDelete)
+            {
+                if (System.IO.File.Exists(file))
+                {
+                    System.IO.File.Delete(file);
+                    _logger.LogDebug("Deleted cache file: {File}", file);
+                }
+            }
+            
+            _logger.LogInformation("✓ Cleared all caches for playlist: {Name}", decodedName);
+            
+            // Trigger rebuild
+            await _matchingService.TriggerMatchingForPlaylistAsync(decodedName);
+            
+            // Invalidate playlist summary cache
+            InvalidatePlaylistSummaryCache();
+            
+            return Ok(new 
+            { 
+                message = $"Cache cleared and rebuild triggered for {decodedName}", 
+                timestamp = DateTime.UtcNow,
+                clearedKeys = cacheKeys.Length,
+                clearedFiles = filesToDelete.Count(System.IO.File.Exists)
+            });
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to clear cache for {Name}", decodedName);
+            return StatusCode(500, new { error = "Failed to clear cache", details = ex.Message });
+        }
+    }
+    
     /// <summary>
     /// Search Jellyfin library for tracks (for manual mapping)
     /// </summary>