refactor: Reorganize repository structure (add initial directories)

[nicholasdbrady]

Description

This pull request reorganizes the repository's file structure to improve clarity and make it easier for developers to find relevant examples based on use cases, providers, or frameworks.

The new top-level structure is:

foundry-samples/ 
├─ use‑cases/ # Examples focused on specific tasks/jobs-to-be-done 
├─ providers/ # Provider-specific examples not tied to a single use case 
└─ frameworks/ # Examples demonstrating specific SDKs or tools

Existing samples and code have not been moved into this new structure. No functional code changes are included in this PR.

Motivation

The previous structure was becoming difficult to navigate as more samples were added. This new organization aims to be more intuitive and scalable.