Ensure collection (config-as-code converge)

Idempotently converge a repo-defined record collection (display fields, schema and validationMode) onto the platform. Identity is slug + account scope. Hash-only probes skip the payload in the steady state (a miss is a normal 200 definitionRequired response); full requests create the collection or update it when the canonical content hash differs. Schema changes follow the same rules as PATCH: they bump schemaVersion and append history, and a breaking change is rejected while the resulting mode is enforce. Set dryRun to plan without writing (CI drift gate), and onConflict: “overwrite” to converge over dashboard/API edits. Ensure never deletes a collection and never touches records.