Refactor project structure and implement new features

- Removed unused security module and updated import paths.
- Enhanced OpenAI client with streaming capabilities for chat completions.
- Added new backend API endpoints for health check (ping).
- Established a new FastAPI application with CORS configuration.
- Created a new Appshell component for the frontend with navigation links.
- Integrated SVG icons and improved styling for the Appshell component.
- Implemented memory management for conversation history using PostgreSQL.
- Developed abstract classes for AI agents and models, with OpenAI integration.
- Added encryption utilities for secure data handling.

frontend/.gitignore

@@ -7,6 +7,9 @@ yarn-error.log*
 lerna-debug.log*
 .pnpm-debug.log*
 
+src/assets/icons/filled/*
+src/assets/icons/outlined/*
+
 # Diagnostic reports (https://nodejs.org/api/report.html)
 report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json