refactor: rename chronos_core -> smriti_core, KAAL -> Smriti throughout backend

Rebrand to Kaal — rename from Chronos OS, add Logo component with serif seal design, swap all Hexagon icons for Logo

Fix lint: Instantiate bearer_scheme in auth.py

Fix 401: Backend now supports both X-API-Key and Authorization: Bearer headers

Initial commit for Chronos OS MVP