Security/codeql research findings

[KevinTran3011]

Summary

Please include a summary of the change and/or which issues are fixed.

eg: Fixes #123 (Tag GitHub issue numbers in this format, so it automatically links the issues with your PR)

List of files changed and why

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How Has This Been Tested?

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Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added/updated unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[KevinTran3011]

Research note: this branch addresses two CodeQL-confirmed issues. (1) CWE-89 / py/sql-injection in the marketplace database helper: table/column identifiers are schema-validated and filter values are bound parameters; endpoint callers no longer build SQL fragments from request data. (2) CWE-918 / py/partial-ssrf in RobotsParser: robots destinations are validated against public DNS addresses and redirects are disabled. Please review the allowed-host policy for deployments that intentionally use private services.