add-component: seed a starter gen-contract.yml and expectations doc once the engine ships #181

Summary

Once specfuse gen-contract ships (specfuse/loop#3536, specfuse/specfuse#225), extend add-component (#180) to seed these files once, alongside the host files:

• gen-contract.yml with generic starter rules for the language: no hand edits under the generated trees, the <auto-generated/> header present on *.g.cs, _generated/ kept out of hand-written imports, and so on. Each rule is green on a fresh seed.
• docs/generated-code-expectations.md, a skeleton with the section names the generator's QA harness reads (clabonte/generator#2885).
• A code gate entry for the check in .specfuse/verification.yml, or printed instructions if the component isn't a loop repo.

The CI drift guard should also run specfuse gen-contract on the seeded component after generation.

Decision record: #171.