Make kept path configurable via web UI

- Added Library:KeptPath to appsettings.json (default: /app/kept)
- Added Library Settings card to web UI with DownloadPath and KeptPath
- Updated GetDownloads and DeleteDownload endpoints to use configured path
- Updated JellyfinController to use configured kept path
- Injected IConfiguration into JellyfinController
- Users can now customize where favorited tracks are stored

allstarr/Controllers/AdminController.cs

@@ -1450,6 +1450,11 @@ public class AdminController : ControllerBase
                 userId = _jellyfinSettings.UserId ?? "(not set)",
                 libraryId = _jellyfinSettings.LibraryId
             },
+            library = new
+            {
+                downloadPath = _configuration["Library:DownloadPath"] ?? "./downloads",
+                keptPath = _configuration["Library:KeptPath"] ?? "/app/kept"
+            },
             deezer = new
             {
                 arl = MaskValue(_deezerSettings.Arl, showLast: 8),
@@ -3331,7 +3336,7 @@ public class LinkPlaylistRequest
     {
         try
         {
-            var keptPath = "/app/kept";
+            var keptPath = _configuration["Library:KeptPath"] ?? "/app/kept";
             
             _logger.LogInformation("📂 Checking kept folder: {Path}", keptPath);
             _logger.LogInformation("📂 Directory exists: {Exists}", Directory.Exists(keptPath));
@@ -3414,7 +3419,7 @@ public class LinkPlaylistRequest
                 return BadRequest(new { error = "Path is required" });
             }
             
-            var keptPath = "/app/kept";
+            var keptPath = _configuration["Library:KeptPath"] ?? "/app/kept";
             var fullPath = Path.Combine(keptPath, path);
             
             _logger.LogInformation("🗑️ Delete request for: {Path}", fullPath);