feat: add -revert mode to restore *.bak back to *.txt

Inverse of -output. For each blog with a TTFolderPath, restores every
*.bak over its *.txt, first preserving the current *.txt as the
next-free *.bkN, then consuming the *.bak. Confirms before running and
supports an optional single-blog filter.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

URLNotesGrabberCORE/Program.cs

@@ -185,6 +185,8 @@ namespace URLNotesGrabberCORE
 
                         Console.WriteLine("-output\t Export posts from TL.db back to .txt files in each blog's TTFolderPath");
 
+                        Console.WriteLine("-revert [blogname]\t Inverse of -output: restore *.bak back to *.txt (current .txt saved as next-free .bkN)");
+
                         Console.WriteLine("-correct [bakPath]\t Dry-run: report multi-line field updates available from a BAK directory");
 
                         Console.WriteLine("-correct -apply [bakPath]\t Apply BAK-file corrections to matching posts (prompts yes/no)");
@@ -329,6 +331,10 @@ namespace URLNotesGrabberCORE
                         OutputMode.Run(config);
                         break;
 
+                    case "-revert":
+                        RevertMode.Run(config, args.Length > 1 ? args[1] : null);
+                        break;
+
                     case "-correct":
                     {
                         bool applyChanges = args.Skip(1).Any(a => string.Equals(a, "-apply", StringComparison.OrdinalIgnoreCase) || string.Equals(a, "--apply", StringComparison.OrdinalIgnoreCase));