fix: escape $ in double-quoted shell descriptions

BugBot: escapeDblQuote was missing $ escaping which is special in
double-quoted bash/fish strings. Add \$ replacement before " to
prevent variable expansion in completion descriptions.

Author: BYK

src/lib/completions.ts

@@ -543,9 +543,9 @@ function escapeSingleQuote(s: string): string {
   return s.replace(/'/g, "'\\''");
 }
 
-/** Escape double quotes and backslashes for fish/bash completion descriptions. */
+/** Escape characters special in double-quoted shell strings (bash/fish). */
 function escapeDblQuote(s: string): string {
-  return s.replace(/\\/g, "\\\\").replace(/"/g, '\\"');
+  return s.replace(/\\/g, "\\\\").replace(/\$/g, "\\$").replace(/"/g, '\\"');
 }
 
 /**