Commit Import To Project

Commit resolved import rows into an EXISTING project (Door 2).

Synchronous — layers exist when the response returns, like the upload endpoint. The request carries references only: the row values come from the held inspect result this server parsed, redeemed by upload.token. Every feature is fenced against projects.county_fips: out-of-county refs are skipped and reported per-row, in-scope rows always commit. Unknown feature ids 404; an expired token 404s; a county-less project can't fence → 422.