Add "Download All in ZIP" feature for session downloads

Introduce automatic ZIP file creation and management for session-based downloads.
- Server: Add endpoints to serve and provide info about session ZIPs; VideoService now updates ZIP after each MP3 download with user-friendly filenames.
- Client: Add "Download All in ZIP" button with loading state and ZIP info; trigger browser download via JS interop; responsive and styled UI.
- API: Extend service interfaces for ZIP download/info; add SessionZipInfo model.
- Docs: Update SESSION_MANAGEMENT.md with ZIP workflow, endpoints, and UX details.
- Robust error handling and logging throughout.

TuneRipper/Pages/Home.razor

@@ -128,6 +128,31 @@
         {
             <div class="download-links-section">
                 <h3 class="downloads-title">📥 Your Downloads</h3>
+                
+                @* Download All in ZIP Button *@
+                @if (!string.IsNullOrWhiteSpace(currentSessionId) && downloadLinks.Count > 1)
+                {
+                    <div class="download-all-container">
+                        <button class="download-all-btn @(isLoadingZip ? "loading" : "")" 
+                                @onclick="DownloadAllInZip" 
+                                disabled="@isLoadingZip">
+                            <span class="download-all-icon">📦</span>
+                            @if (isLoadingZip)
+                            {
+                                <span>Preparing ZIP...</span>
+                            }
+                            else
+                            {
+                                <span>Download All in ZIP</span>
+                            }
+                            @if (sessionZipInfo != null)
+                            {
+                                <span class="zip-info">(@sessionZipInfo.Mp3FilesCount files, @sessionZipInfo.FileSize)</span>
+                            }
+                        </button>
+                    </div>
+                }
+                
                 <div class="download-links">
                     @foreach (var download in downloadLinks.AsEnumerable().Reverse())
                     {
@@ -168,11 +193,13 @@
     private string outputMessage = "";
     private string apiErrorMessage = "";
     private bool isProcessing = false;
+    private bool isLoadingZip = false;
     private int progressPercentage = 0;
     private string progressMessage = "";
     private List<DownloadItem> downloadLinks = new();
     private YouTubeVideoDetails? currentVideoDetails = null;
     private string currentSessionId = "";
+    private SessionZipInfo? sessionZipInfo = null;
 
     public class DownloadItem
     {
@@ -189,6 +216,10 @@
             // Initialize session on component load
             currentSessionId = await SessionService.GetCurrentSessionIdAsync();
             Logger.LogInformation("Initialized with session: {SessionId}", currentSessionId);
+            
+            // Load session ZIP info if available
+            await LoadSessionZipInfoAsync();
+            
             StateHasChanged();
         }
         catch (Exception ex)
@@ -198,6 +229,58 @@
         }
     }
 
+    private async Task LoadSessionZipInfoAsync()
+    {
+        try
+        {
+            if (!string.IsNullOrWhiteSpace(currentSessionId))
+            {
+                sessionZipInfo = await ApiService.GetSessionZipInfoAsync(currentSessionId);
+            }
+        }
+        catch (Exception ex)
+        {
+            Logger.LogError(ex, "Error loading session ZIP info");
+            // Don't block the UI if ZIP info loading fails
+        }
+    }
+
+    private async Task DownloadAllInZip()
+    {
+        if (string.IsNullOrWhiteSpace(currentSessionId))
+        {
+            apiErrorMessage = "Session not available for ZIP download";
+            return;
+        }
+
+        try
+        {
+            isLoadingZip = true;
+            StateHasChanged();
+
+            Logger.LogInformation("Downloading session ZIP for session: {SessionId}", currentSessionId);
+
+            // Create the download URL for the ZIP file
+            var zipDownloadUrl = $"https://localhost:7160/api/download/zip/{currentSessionId}";
+            
+            // Use browser to download the ZIP file
+            await JSRuntime.InvokeVoidAsync("open", zipDownloadUrl, "_blank");
+            
+            Logger.LogInformation("Successfully initiated ZIP download for session: {SessionId}", currentSessionId);
+        }
+        catch (Exception ex)
+        {
+            Logger.LogError(ex, "Error downloading session ZIP for session: {SessionId}", currentSessionId);
+            apiErrorMessage = $"Error downloading ZIP file: {ex.Message}";
+            StateHasChanged();
+        }
+        finally
+        {
+            isLoadingZip = false;
+            StateHasChanged();
+        }
+    }
+
     private async Task DownloadMp3()
     {
         if (!string.IsNullOrWhiteSpace(youtubeUrl))
@@ -377,6 +460,9 @@
             progressPercentage = 100;
             progressMessage = "Complete!";
             
+            // Reload session ZIP info after successful download
+            await LoadSessionZipInfoAsync();
+            
             // Small delay to show completion
             await Task.Delay(500);