feat: landing page + logo, dev-mode banner + sync cap, non-blocking sync with progress splash

src/InboxIntel.Application/Abstractions/IServices.cs

@@ -9,7 +9,11 @@ public interface ISyncService
 {
     Task RunFullSyncAsync(Guid userId, CancellationToken ct = default);
     Task RunIncrementalSyncAsync(Guid userId, CancellationToken ct = default);
+    /// <summary>Marks the sync as starting and queues it for the background worker.</summary>
+    Task QueueSyncAsync(Guid userId, bool fullSync, CancellationToken ct = default);
     Task<SyncStatus> GetStatusAsync(Guid userId, CancellationToken ct = default);
+    /// <summary>Progress snapshot for the sync splash screen.</summary>
+    Task<DTOs.SyncProgressDto> GetProgressAsync(Guid userId, CancellationToken ct = default);
 }
 
 public interface IAnalyticsService

src/InboxIntel.Application/Abstractions/ISyncQueue.cs

@@ -0,0 +1,10 @@
+namespace InboxIntel.Application.Abstractions;
+
+/// <summary>
+/// Hands sync work to a background worker so HTTP triggers return immediately
+/// and the UI can poll progress (non-blocking architecture).
+/// </summary>
+public interface ISyncQueue
+{
+    void Enqueue(Guid userId, bool fullSync);
+}

src/InboxIntel.Application/DTOs/SyncDtos.cs

@@ -0,0 +1,13 @@
+namespace InboxIntel.Application.DTOs;
+
+/// <summary>
+/// Live sync progress for the splash screen. <see cref="Total"/> reflects the
+/// dev cap when one is configured, so the progress bar fills correctly.
+/// </summary>
+public record SyncProgressDto(
+    string Status,
+    int Processed,
+    int Total,
+    bool IsRunning,
+    DateTimeOffset? LastSuccessfulSyncUtc,
+    string? LastError);