Fix architecture section in root README to match actual code layout

[observerr411]

• Location: README.md:27-33
• Problem: README lists file names like patient_registry.rs/provider_registry.rs that do not match this monorepo's crate-based structure under contracts/.
• Resolution criteria: Rewrite architecture docs to map to real crate directories and public contract names.

[AdityaK9822]

@AdityaK9822 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

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I would like to work on this issue.

I’ll update the architecture section in the README to accurately reflect the current crate-based structure under the contracts/ directory, ensuring all modules and contract names align with the actual repository layout.

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[Enemuo-debug]

@Enemuo-debug has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Can I work on this???

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