fix(tools): escape backslash characters in markdown output

Address CodeQL security alert by escaping backslash characters before
escaping other special markdown characters. This prevents incomplete
escaping when input contains backslashes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dcramer

packages/mcp-core/src/tools/get-issue-tag-values.ts

@@ -159,8 +159,9 @@ export default defineTool({
         value.value.length > 60
           ? `${value.value.substring(0, 57)}...`
           : value.value;
-      // Escape markdown table special characters
+      // Escape markdown table special characters (backslashes first)
       displayValue = displayValue
+        .replace(/\\/g, "\\\\")
         .replace(/\|/g, "\\|")
         .replace(/`/g, "\\`")
         .replace(/\n/g, " ");