fix: replace all non-ASCII progress markers for Windows encoding

Also fix miner.py checkmark and box-drawing/arrow chars (─, →) in
both miner.py and split_mega_files.py that would crash on cp1251/cp1252.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

mempalace/split_mega_files.py

@@ -290,7 +290,7 @@ def main():
     print(f"  Source:      {src_dir}")
     print(f"  Output:      {output_dir or 'same dir as source'}")
     print(f"  Mega-files:  {len(mega_files)}")
-    print(f"{'─' * 60}\n")
+    print(f"{'-' * 60}\n")
 
     total_written = 0
     for f, n_sessions in mega_files:
@@ -301,11 +301,11 @@ def main():
         if not args.dry_run and written:
             backup = f.with_suffix(".mega_backup")
             f.rename(backup)
-            print(f"  → Original renamed to {backup.name}\n")
+            print(f"  -> Original renamed to {backup.name}\n")
         else:
             print()
 
-    print(f"{'─' * 60}")
+    print(f"{'-' * 60}")
     if args.dry_run:
         print(f"  DRY RUN — would create {total_written} files from {len(mega_files)} mega-files")
     else: