🛡️ Sentinel: [MEDIUM] Fix bare except DoS risk

[NoWon1]

🚨 Severity: MEDIUM
💡 Vulnerability: Bare except: blocks catch BaseException (including SystemExit and KeyboardInterrupt). This masks system signals and prevents safe shutdowns or process termination.
🎯 Impact: System processes might hang and cannot be stopped with keyboard interrupts, representing a localized Denial of Service (DoS) and robustness risk.
🔧 Fix: Replaced all instances of except: with except Exception: across CancerInvasionSteppables.py.
✅ Verification: Ran bandit security linter which no longer flags [B112:try_except_continue] warnings. Tested python compile. Also added a .gitignore to prevent cache binaries from being tracked, and updated .jules/sentinel.md with learnings.

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PR created automatically by Jules for task 17714114259633685278 started by @NoWon1

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