🛡️ Sentinel: [HIGH] Prevent path traversal in mod name and version validation

[TheDragonSoft]

🚨 Severity: HIGH
💡 Vulnerability: plausible_name and plausible_version accepted ., .., and strings containing .. sequences.
🎯 Impact: Malicious mod names or versions containing .. could cause path traversal issues when constructed into file paths or API endpoints.
🔧 Fix: Explicitly reject ., .., and strings containing .. in plausible_name and plausible_version.
✅ Verification: Ran cargo test (142 unit tests passed, including new path traversal validation tests) and pnpm build.

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PR created automatically by Jules for task 3284721269290791542 started by @TheDragonSoft

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