Create a valuation widget key

Creates a publishable widget key bound to one to five exact origins when the authenticated client has valuations.embed_keys.write. An origin is a scheme, host and optional port with no path, such as https://www.example.com; plain HTTP is accepted only for localhost and 127.0.0.1. An organization may hold 10 active keys per environment; beyond that the route answers 429 valuation_embed_key_quota_exceeded. External URL: /v1/valuations/embed-keys. Current Next.js implementation path: /api/platform/v1/valuations/embed-keys. This mutating route requires Idempotency-Key and records an audit event. A widget key is publishable, not a secret: it ships in the partner page and works only on the free public valuation routes, from its registered origins, with a cap of 2,000 estimates a day per key. It never authenticates this API.