fix: Q4 simultaneous-placement fix across env, models, privacy, data_loader

feat: Q4 Gauntlet extension -- Tasks 5/6/7, phase controller, training pipeline

feat: Priority 2-5 complete — env mechanics, simulate endpoint, grader quality, tests, docs

feat: Task 4 Adversarial Regulator + confidence_interval

deploy: Meta-Signal environment -- all 5 layers