Avoid no-op Current Host catalog generations

[ian-pascoe]

Problem

The shared catalog update path validates requested IDs, clones the active snapshot, and commits a new generation even when no authority record changes. This creates needless cross-replica activation, receipts, and activity for a semantic no-op.

Acceptance criteria

• Catalog update resolves/materializes changed bundles before commit.
• If every requested record is unchanged, return an unchanged/current outcome without publishing a generation.
• Changed updates still use generation CAS/idempotency and preserve staged-ID reservation.
• Tests cover all-unchanged, mixed changed/unchanged, replay, and concurrent conflict behavior.

Evidence

Review anchor: packages/core/src/current-host/catalog-operations.ts around sharedCatalogUpdateOutcome (~267-305).