refactor: restructure project as uqlm-guard with enhanced core engine

- Rename gate/ to uqlm_guard/ for better branding
- Implement detailed uncertainty analysis in core/analyzer.py
- Add comprehensive inconsistency detection
- Introduce consensus and divergence analysis
- Create Pydantic models for type safety
- Support multi-sample UQLM-based scoring

Breaking change: Package renamed from gate to uqlm_guard

Author: Kelpejol