🔒 Fix ReDoS vulnerability in pipe_to_shell regex

[google-labs-jules]

🎯 What: Fixed a ReDoS vulnerability in the pipe_to_shell regex inside hooks/security_guard.py.
⚠️ Risk: A long sequence of space characters combined with the overlapping \s+ and .* capture groups could trigger exponential backtracking ($O(N^2)$), causing the regex engine to hang and denying service to the hook process.
🛡️ Solution: Changed the regex from \s+.*\| to \s[^|]*\|. This exactly matches at least one whitespace character (\s) while letting the negated character class [^|]* deterministically consume any remaining characters (including spaces) up to the pipe character |, thereby eliminating overlapping backtracking paths.

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PR created automatically by Jules for task 17491394274003151515 started by @zknpr

[google-labs-jules]

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