Fix title attribute unescaping to handle \\" and \" only

The previous unescape only handled \", missing \\. Use /\\(["\\])/
to correctly unescape both without affecting other backslash sequences
like literal \n in samplecode labels.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: znz

lib/bitclust/markdown_to_rrd.rb

@@ -151,7 +151,7 @@ def convert_code_block(line)
         lang = $2.empty? ? nil : $2
       end
       if line =~ /title="((?:[^"\\]|\\.)*)"/
-        title = $1.gsub('\\"', '"')
+        title = $1.gsub(/\\(["\\])/, '\1')
       end
 
       if lang == 'ruby'

test/test_markdown_to_rrd.rb

@@ -108,6 +108,12 @@ def test_code_block_without_language
     assert_equal expected, convert(md)
   end
 
+  def test_code_block_title_with_backslash
+    md = "```ruby title=\"C:\\\\path\"\ncode\n```\n"
+    expected = "\#@samplecode C:\\path\ncode\n\#@end\n"
+    assert_equal expected, convert(md)
+  end
+
   def test_code_block_lang_without_title
     md = "```sh\necho hello\n```\n"
     expected = "//emlist[][sh]{\necho hello\n//}\n"