acq doctor should report a missing provider-input validator runtime #645

Since #608 every OpenCode acq create validates provider inputs, and since #619 a git checkout must run scripts/setup-provider-input-validator --apply --online once. The only place acq checks for the runtime is inside create (_acq_provider_input_python), so a host that pulled past #608 learns about the new prerequisite from a failed create. For callers that remove a sandbox and re-create it under the same name (a recreate script, acq rm + acq create), the sandbox is already gone when create fails.

Ask: have acq doctor (no NAME) report whether the validator runtime is present and usable, with the same remedy text create prints (--apply --online for a git checkout, reinstall for a release install), and exit non-zero when it's missing, so wrappers can run it as a preflight.

Seen 2026-10-26: a teammate on a quickstart git checkout at main ran a recreate, which removed the sandbox, then failed with provider-input validator wheelhouse is missing / provider input projection failed.