List sandbox partner site forms

Returns deterministic sandbox partner-site form metadata when the authenticated automation client has forms.read. External URL: /v1/sites/{id}/forms. Current Next.js implementation path: /api/platform/v1/sites/[id]/forms. This read-only route does not require Idempotency-Key; it returns form metadata only and never returns submissions, exposes recipient destinations, renders public forms, publishes sites, writes CRM records, performs scheduling side effects, configures custom domains, calls providers, or exposes partner secrets. Live site form reads remain unavailable until ownership, consent, delivery, and route-promotion gates pass.