Add file-based caching for admin UI and fix Jellyfin API usage

- Added 5-minute file cache for playlist summary to speed up admin UI loads
- Added refresh parameter to force cache bypass
- Invalidate cache when playlists are refreshed or tracks are matched
- Fixed incorrect use of anyProviderIdEquals (Emby API) in Jellyfin
- Now searches Jellyfin by artist and title instead of provider ID
- Fixes 401 errors and 'no client headers' warnings in lyrics prefetch
- All 225 tests passing

allstarr/Controllers/AdminController.cs

@@ -211,8 +211,40 @@ public class AdminController : ControllerBase
     /// Get list of configured playlists with their current data
     /// </summary>
     [HttpGet("playlists")]
-    public async Task<IActionResult> GetPlaylists()
+    public async Task<IActionResult> GetPlaylists([FromQuery] bool refresh = false)
     {
+        var playlistCacheFile = "/app/cache/admin_playlists_summary.json";
+        
+        // Check file cache first (5 minute TTL) unless refresh is requested
+        if (!refresh && System.IO.File.Exists(playlistCacheFile))
+        {
+            try
+            {
+                var fileInfo = new FileInfo(playlistCacheFile);
+                var age = DateTime.UtcNow - fileInfo.LastWriteTimeUtc;
+                
+                if (age.TotalMinutes < 5)
+                {
+                    var cachedJson = await System.IO.File.ReadAllTextAsync(playlistCacheFile);
+                    var cachedData = JsonSerializer.Deserialize<Dictionary<string, object>>(cachedJson);
+                    _logger.LogDebug("📦 Returning cached playlist summary (age: {Age:F1}m)", age.TotalMinutes);
+                    return Ok(cachedData);
+                }
+                else
+                {
+                    _logger.LogDebug("🔄 Cache expired (age: {Age:F1}m), refreshing...", age.TotalMinutes);
+                }
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to read cached playlist summary");
+            }
+        }
+        else if (refresh)
+        {
+            _logger.LogInformation("🔄 Force refresh requested for playlist summary");
+        }
+        
         var playlists = new List<object>();
         
         // Read playlists directly from .env file to get the latest configuration
@@ -541,6 +573,24 @@ public class AdminController : ControllerBase
             playlists.Add(playlistInfo);
         }
         
+        // Save to file cache
+        try
+        {
+            var cacheDir = "/app/cache";
+            Directory.CreateDirectory(cacheDir);
+            var cacheFile = Path.Combine(cacheDir, "admin_playlists_summary.json");
+            
+            var response = new { playlists };
+            var json = JsonSerializer.Serialize(response, new JsonSerializerOptions { WriteIndented = false });
+            await System.IO.File.WriteAllTextAsync(cacheFile, json);
+            
+            _logger.LogDebug("💾 Saved playlist summary to cache");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Failed to save playlist summary cache");
+        }
+        
         return Ok(new { playlists });
     }
     
@@ -872,6 +922,10 @@ public class AdminController : ControllerBase
     {
         _logger.LogInformation("Manual playlist refresh triggered from admin UI");
         await _playlistFetcher.TriggerFetchAsync();
+        
+        // Invalidate playlist summary cache
+        InvalidatePlaylistSummaryCache();
+        
         return Ok(new { message = "Playlist refresh triggered", timestamp = DateTime.UtcNow });
     }
     
@@ -892,6 +946,10 @@ public class AdminController : ControllerBase
         try
         {
             await _matchingService.TriggerMatchingForPlaylistAsync(decodedName);
+            
+            // Invalidate playlist summary cache
+            InvalidatePlaylistSummaryCache();
+            
             return Ok(new { message = $"Track matching triggered for {decodedName}", timestamp = DateTime.UtcNow });
         }
         catch (Exception ex)
@@ -3126,6 +3184,30 @@ public class AdminController : ControllerBase
     }
     
     #endregion
+    
+    #region Helper Methods
+    
+    /// <summary>
+    /// Invalidates the cached playlist summary so it will be regenerated on next request
+    /// </summary>
+    private void InvalidatePlaylistSummaryCache()
+    {
+        try
+        {
+            var cacheFile = "/app/cache/admin_playlists_summary.json";
+            if (System.IO.File.Exists(cacheFile))
+            {
+                System.IO.File.Delete(cacheFile);
+                _logger.LogDebug("🗑️ Invalidated playlist summary cache");
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Failed to invalidate playlist summary cache");
+        }
+    }
+    
+    #endregion
 }
 
 public class ManualMappingRequest