fix(upload_security): Refine extractors to reduce false positives

[google-labs-jules]

What

Refines UploadSecurityExtractor regexes and heuristics to avoid flagging benign code paths.

Why

• The KEY_FROM_NAME pattern matched originalname even when used inside log strings or unconnected statements. Fixed by tightening bounds.
• The TRUST_CLIENT_MIME pattern matched mimetype calls inside console.log and logger.info, which are not security sinks. Handled with a local _is_safe_mime heuristic.
• The serve-no-nosniff flagged res.sendFile('/absolute/path') or res.sendFile('file', { root: 'public' }) which denote hardcoded static content rather than arbitrary user uploads. Resolved by skipping fully static literals in arguments.

Risk

Low. Modifications are bounded string/AST-heuristic refinements, heavily constrained by regression tests (test_upload_key_fp_string_match, test_upload_trust_client_mime_log_fp, test_upload_serve_static_string_fp) added in tests/test_pentest_regressions.py. All RemainingControlScopeTests continue to pass.

---

PR created automatically by Jules for task 8865206105426281740 started by @raccioly

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.

[github-actions]

Held for human review.

touches src/websec_validator/extractors/upload_security.py (protected path)

CI is green; the merge gate stops here on scope, not on test results. Merge it yourself if the change is what you want.