Add Pivot Engine - deterministic mutation-based security testing

[Insider77Circle]

Summary

• Introduces the Pivot subsystem: a structured, deterministic mutation engine for HTTP security testing
• Adds baseline capture, response delta analysis, and anomaly buffering for behavioral fingerprinting
• Implements encoding and structural mutators with a family registry for organized mutation strategies
• Includes deterministic scoring engine and signal rule matching via YAML-configurable rule sets
• Adds pattern-signature and signal-rule config files for extensible detection logic

Components

Module	Purpose
src/pivot/PivotEngine.ts	Core orchestration engine
src/pivot/PivotEngineWired.ts	Wired variant with integrated dependencies
src/pivot/baseline/	Baseline capture, response deltas, anomaly buffering
src/pivot/http/	HTTP executor for probe dispatch
src/pivot/mutation/	Encoding & structural mutators, family registry
src/pivot/scoring/	Deterministic scorer, signal rule registry
src/types/pivot.ts	TypeScript type definitions
configs/	YAML rule and signature configs

Test plan

• Verify TypeScript compilation with tsc --noEmit
• Run mutation test harness via test-mutations.ts
• Validate YAML config loading for signal rules and pattern signatures
• End-to-end pivot engine run against a test target