Update docs: fix Dexie version, add directory structure, changelog v2.1.0/v2.1.1, resolved issues

- DOCS.md: Fix Dexie v3→v5 references (3 places), add 5 missing DB tables,
  add 4 missing API endpoints, Emotion Match→Quiz, 6 new resolved issues
  (R18-R23), v2.1.0 + v2.1.1 changelog, full project directory tree
- README.md: Fix BetterAuth→Google OAuth, update project structure,
  add missing biomarker fields, update identity strategy

Author: Partha-dev01