Create Keys Bulk

Batch key creation — idempotent, best-effort per-item. Batches the writes only; there is NO server-side translation.

Valid items commit even when siblings fail; each item gets an entry in results (status ok|error) plus a roll-up summary. Unknown namespace and intra-batch duplicates (same namespace+name twice) error per item. The plan key-cap is a whole-batch gate: if the NEW keys would push the org over its cap the entire call is rejected (403) before any write.