feat(approvals): add policy-gated batch decisions for homogeneous low-risk requests #403

Parent: #361

Why this remains open

Bulk decisions reduce review overhead but must not turn a selection gesture into a broad approval. The current queue lacks a server-side batch contract and a policy classification that can prove every selected item is safe to combine.

Scope

• Server computes eligibility per item and rejects mixed-source, expired, conflicting, write/delete, external-network, or otherwise unsafe batches.
• Batch requests retain each item's expected version and durable, per-item audit result.
• UI shows the exact count, source boundary, and items excluded by policy before submitting.

Acceptance criteria

• A batch cannot broaden the action, scope, or expiry of any member.
• Partial conflicts are reported per item without silently deciding others.
• Idempotency/retry cannot duplicate a verdict.
• Tests cover allowed homogeneous low-risk sets and every disallowed boundary.