🛡️ Sentinel: [HIGH] Fix path traversal and prefix bypass vulnerabilities

[hackerxj2010]

🛡️ Sentinel has identified and fixed two critical path-related vulnerabilities:

1. Path Traversal in LocalJsonStore: The LocalJsonStore was vulnerable to path traversal through .. injection in keys. I've updated toPath to explicitly block these segments and perform a robust absolute path prefix check to ensure all file operations stay within the base directory.
2. Prefix Bypass in TerminalService: The resolveCwd method used a naive startsWith check which was vulnerable to prefix bypass (e.g., /workspace-secret would match an allowed /workspace). I've implemented a ensureTrailingSep helper to ensure correct directory-level containment checks.

Both fixes have been verified with new and updated unit tests, and the full test suite passes.

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PR created automatically by Jules for task 4939822673830252959 started by @hackerxj2010

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