fix: eliminate false positives in UploadSecurityExtractor

[google-labs-jules]

What

Tightened regex for upload_security extractor to avoid flagging log messages, internal file streams, and independent metadata keys. Added 5 permanent regression tests in test_pentest_regressions.py asserting these false positive scenarios are successfully suppressed.

Why

This addresses several FPs where normal diagnostic logging or internal S3 read streams triggered high-severity warnings (KEY_FROM_NAME, TRUST_CLIENT_MIME, SERVE_FILE).

Risk

Low. Existing tests and true positive fixtures continue to pass. The regex tightening is precise, e.g., restricting KEY_FROM_NAME property matching to stop spanning across commas, and ensuring TRUST_CLIENT_MIME matches assignments and comparisons but skips template literals passed to logging.

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PR created automatically by Jules for task 6323615530875403716 started by @raccioly

[google-labs-jules]

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