docs: fix CONTRIBUTING first-run path and crate map

[Tuntii]

A first-time contributor following CONTRIBUTING.md tonight hits a dead path.

CONTRIBUTING.md still says ls examples/ and cargo run -p hello-world. Those packages are gone. The live path is:

cargo run -p rustapi-rs --example golden_path

Please:

• Point Running Examples at crates/rustapi-rs/examples/ and the golden_path command above
• Refresh the project-structure tree so it matches crates/ (include rustapi-mcp, rustapi-grpc, rustapi-testing; drop the old root examples/ layout)

No code changes. Docs only. See docs/GOLDEN_PATH.md for the intended first run.