Propose Translations Bulk

Batch translation upserts — idempotent, best-effort per-item, with write-through key auto-create. Batches the writes only; the values come from the caller (NO server-side translation).

Per-item results (status ok|unchanged|error) + summary. An item whose value AND status already match the stored row returns status unchanged (no version bump, no history). reviewed/approved are rejected per item. Unknown namespace/language and intra-batch duplicates error per item. No plan-cap gate here: the write-through auto-create mirrors the single propose path (the cap gap on that path is scoped separately).