feat: Implement Supabase client initialization, including environment variable validation and a connectivity test.

feat: add Supabase client initialization with environment variable validation.

feat: Implement secure data storage and retrieval services with encryption/decryption and add local mock tests for API endpoints.

feat: Add secure message storage and retrieval via Supabase with burn and retrieval limit options.

refactor: modularize application by extracting core logic into dedicated services, security, database, and router modules.

feat: Implement encrypted data storage and retrieval endpoints using FastAPI and cryptography, and update the README.