feat: add token usage tracking for AI recommendations and subscription management

feat: add subscription management with user plan tracking and response schema

Remove compiled Python cache files from backend and tests

Add chat conversations and try-on history endpoints

Update .gitignore to include specific __pycache__ directories and adjust patterns for Python files

feat: add chest, waist, and hips measurements support in profile and LLM service

feat: integrate local CatVTON virtual try-on and secure env files

Initialize production-grade FastAPI backend with models, routes, celery workers, and test suite