feat: 🚀 add multi-backend support and strict TypeScript guidelines

- **✨ Features**
  - Implement multi-backend orchestration to support model aggregation and namespacing across multiple LiteLLM instances.
  - Introduce a comprehensive TypeScript "No-Any" policy to enforce strict type safety and eliminate technical debt.
- **📦 Documentation**
  - Add the full LiteLLM OpenAPI specification to serve as a foundational reference for proxy API integrations.
  - Update the changelog and agent documentation to reflect version 1.6.0-dev milestones and architectural standards.
- **🧹 Chores**
  - Upgrade Codecov CI action to v6 and remove unused extensions from the development container configuration.
  - Implement a post-session validation hook to automate execution of verification scripts.