fix: [#437] restore third-party Trivy SARIF uploads

[josecelano]

Summary

Fix the Docker security scanning workflow so third-party Trivy SARIF results are uploaded through a supported path.

Changes

• Add security-events: write permission to scan-third-party-images
• Upload third-party SARIF directly with github/codeql-action/upload-sarif@v4
• Use stable per-image categories: docker-third-party-${sanitized-image}
• Remove the unsupported custom gh api /code-scanning/sarifs upload loop
• Restrict aggregate uploader to project SARIF artifacts only

Why

The previous custom upload was failing with HTTP 422 ("category" is not a permitted key) and silently skipping third-party uploads, which caused PR warnings like configurations not found.

Validation

• cargo run --bin linter yaml passes

Closes #437

[josecelano]

ACK b397688

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