feat(core): initialize cargo workspace and module structure (#5)

[ZhuchkaTriplesix]

Summary of Changes

• Initialized Cargo.toml with required dependencies (tokio, serde, serde_json, secrecy, tracing, thiserror, reqwest, etc.).
• Set up modular folder structure: src/{transport, rpc, driver, mapper, sdui, utils}/mod.rs along with error.rs, config.rs, and main.rs.
• Added manifest.json conforming to Querya Block E Sandbox specification (256MB RAM, connection_host_only, secretsStore).
• Created placeholder assets/icon.svg and assets/connection_form.json.
• Configured .gitignore to exclude /target/ and build artifacts.

Closes #5