Add SARIF export and audit filtering controls

[haizen1312]

Goal

Make Repository Audit Lab interoperable with standard developer security workflows.

Scope

• SARIF 2.1.0 export
• confidence threshold control
• .gitignore-aware client filtering
• deterministic fix suggestions for common SQL, TLS and DOM XSS review patterns
• regression tests for JSON and SARIF output

Safety

Static defensive analysis only. Do not execute uploaded code, install dependencies or generate exploit payloads.

Acceptance

A user can export a valid SARIF file that imports into GitHub code scanning-compatible viewers.