fix: use exact word boundary in built-in module check

grep -q "^re" was matching 'requests' since it starts with 're'.
Use a regex that requires the module name to be followed by a
version specifier, whitespace, or end-of-line.

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

Author: surpradhan

.github/workflows/lint.yml

@@ -107,7 +107,7 @@ jobs:
 
         # Check for built-in modules listed as dependencies
         for builtin in ast difflib json re sys os subprocess; do
-          if grep -q "^$builtin" requirements*.txt; then
+          if grep -qE "^${builtin}([[:space:]>=<!]|$)" requirements*.txt; then
             echo "Error: $builtin is a built-in module, should not be in requirements"
             exit 1
           fi