feat: update subscription response to track AI credits instead of tokens

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

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

Add chat conversations and try-on history endpoints

Add virtual try-on for Marketplace and Dashboard items

Switch try-on and garment analysis to external image APIs

feat: implement conversational chatbot with routing and chat history support

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