AI plausibility review

Every registration triggers two AI checks:

• Pre-flight review — runs on the draft before the on-chain tx. If the listing has placeholder text, is empty, or contains obvious spam, the registrant is warned. Red verdicts require an explicit override checkbox to proceed.
• Post-registration review — runs automatically after the listing lands. The verdict, summary, and specific flags are attached to the listing's dashboard and displayed as an AI · Sus or AI · Flagged badge on the registry cards.