fix(chains): deduplicate LLM prompt injection chains to prevent duplicates

fix: resolve logic, security, and memory leak issues in scanner layers

refactor(backend): use asyncio and thread pools for background tasks, optimize scanner AST utils and checks

feat: Upgrade taint analysis agent and exploit chain correlator with advanced security reasoning

feat(pipeline): VibeSec Elite master upgrades and operational sweep

feat: secure Python backend engine v2.0