chore: log folder transitions during -ingest

The every-50-file progress line wasn't enough to know which blog was
currently being processed on a long run. Now -ingest prints a
"entering folder: <name>" line whenever the source folder changes, and
the every-50 progress line also prefixes the folder name.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

URLNotesGrabberCORE/IngestMode.cs

@@ -72,6 +72,7 @@ namespace URLNotesGrabberCORE
             int filesProcessed = 0;
             int filesSkipped = 0;
             int postsTouched = 0;
+            string? lastBlogFolder = null;
 
             try
             {
@@ -93,8 +94,16 @@ namespace URLNotesGrabberCORE
                         }
 
                         filesProcessed++;
-                        if (filesProcessed % 50 == 0 || filesProcessed == 1)
-                            Console.WriteLine($"[{filesProcessed}/{txtFiles.Count}] {Path.GetFileName(file)}");
+
+                        if (lastBlogFolder != rawBlogName)
+                        {
+                            Console.WriteLine($"[{filesProcessed}/{txtFiles.Count}] >> entering folder: {rawBlogName}");
+                            lastBlogFolder = rawBlogName;
+                        }
+                        else if (filesProcessed % 50 == 0)
+                        {
+                            Console.WriteLine($"[{filesProcessed}/{txtFiles.Count}] {rawBlogName}/{Path.GetFileName(file)}");
+                        }
 
                         string currentPostId = "";
                         var currentPostData = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);