Task: Add batch support for saves and deletes

Make save + delete atomic at the batch level.

• save_*_request takes std::vector<entity>; save_*_response returns /{success, message/} (single outcome).
• Batch delete uses SQL WHERE IN (...) for atomicity across 23 entities in ores.dq, ores.refdata, ores.trading, ores.iam.
• Repository, service, and message-handler layers all align with the new shape.
• Temporal guard for IAM entities (tenant_type, tenant_status) — valid_to = max constraint preserves historical rows.
• save_result.hpp introduced then later removed as dead code.
• Protocol 46.0 (breaking).

Captured during execution; cleared into the parent story on close.

Closes a class of partial-write bugs and aligns repository / service / handler conventions.

Batch operations atomic.