fix: escape parens and braces in fork bomb regex pattern

The fork bomb regex used `()` (empty capture group) and unescaped `{}`
instead of literal `\(\)` and `\{\}`. This meant the classic fork bomb
`:(){ :|:& };:` was never detected. Also added `\s*` between `:` and
`&` and between `;` and trailing `:` to catch whitespace variants.

tools/approval.py

@@ -38,7 +38,7 @@ DANGEROUS_PATTERNS = [
     (r'\bsystemctl\s+(stop|disable|mask)\b', "stop/disable system service"),
     (r'\bkill\s+-9\s+-1\b', "kill all processes"),
     (r'\bpkill\s+-9\b', "force kill processes"),
-    (r':()\s*{\s*:\s*\|\s*:&\s*}\s*;:', "fork bomb"),
+    (r':\(\)\s*\{\s*:\s*\|\s*:\s*&\s*\}\s*;\s*:', "fork bomb"),
     (r'\b(bash|sh|zsh)\s+-c\s+', "shell command via -c flag"),
     (r'\b(python[23]?|perl|ruby|node)\s+-[ec]\s+', "script execution via -e/-c flag"),
     (r'\b(curl|wget)\b.*\|\s*(ba)?sh\b', "pipe remote content to shell"),