Reject malformed projects.create() inputs at the door instead of hanging

One instance was observed in the wild:

itx.projects.create({ name: "…" }) (wrong key — the contract wants slug) is not rejected; the call proceeds and hangs the full 60s ready-wait, looking EXACTLY like a broken deployment (this burned an hour of prd bisection on 2026-07-17 after #2048's merge).

What to do#

• Strict input validation on projects.create (unknown keys / missing slug → immediate contract error naming the field).

This is a door check: fail fast with a nameable error, never a timeout that impersonates an outage.