🛡️ Sentinel: [CRITICAL/HIGH] Fix command option injection

[dttdrv]

🚨 Severity: CRITICAL/HIGH
💡 Vulnerability: The mainFile parameter in CompileQueueService was passed directly as a positional argument to latexmk within the Rust compile worker. A user could supply a file name starting with a hyphen (e.g., -shell-escape or -output-directory=...), which latexmk would interpret as an executable flag instead of a file name.
🎯 Impact: Unsanitized file names could allow an attacker to inject arbitrary flags into latexmk, leading to remote code execution (via -shell-escape) or arbitrary file operations (via -output-directory).
🔧 Fix: Added a validation check in backend/src/services/compileQueue.ts to reject any request.mainFile that starts with a hyphen (-).
✅ Verification: Ran npx vitest run to ensure tests passed. The validation throws a standard 400 HttpError when a hyphen is provided.

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PR created automatically by Jules for task 11608252281840772252 started by @dttdrv

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