Introduce ExpressionFactory grammar generator, store raw result payload in DB, and handle incomplete/timeout simulation statuses

Phase 7: Analytics dashboard overhaul - trash_reason tracking, enriched /api/stats, Semaphore(11), premium dark/light UI, LLM router model tracking, pause/resume endpoints

Restore backwards compatibility for legacy app.py and submission_engine.py by adding SessionLocal and compatibility fields

QuantForge v2.0 Phase 1 & 2: Core Async client, models, configuration, and Agentic Generation Layer