bug fix for dynamic routing logic

chore: add structured logging across backend

chore: clean DB, enable static mount, update env for deploy

updated ui, docs, tests

feat: register batches, topics, upload routers in main.py

fix: auth quality issues — token cleanup, delete_cookie params, broad exception catch, dead import

feat: implement auth router (signup/login/refresh/logout) and FastAPI deps

chore: add backend directory structure and stub files