Fix VibeSec pipeline logic bugs, routing, feedback store, and RLS test cases

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

fix(feedback): resolve rule_fp_rates SQLite table initialization crash

feat(scanner): implement 5 targeted improvements to scanning engine and rules

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

feat(scanner): sync dynamic secrets validation filters and entropy triaging

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

feat: secure Python backend engine v2.0