Keep adapter-specific maxTurnsPerRun (default 1000) in the config
schema since the platform UI does not provide it for external adapters.
Platform-provided fields (model, effort, instructionsFilePath,
timeoutSec, graceSec) remain excluded to avoid duplication.
Add config-schema.test.ts with assertions that platform-provided
fields are absent and adapter-specific fields have correct defaults.
Co-Authored-By: Paperclip <noreply@paperclip.ing>
