feat(offline): share read settlement metadata

[rdlabo]

Summary

• add a shared OfflineReadEmission<T> contract for local-first reads
• expose a generic response-completeness header alongside the existing source header
• add helpers that convert HttpResponse metadata and safely settle collection UI state

Why

Products using Kit's local-first reads otherwise need to duplicate source-header parsing and the rule that an incomplete empty local collection must not clear usable state. Product policies still own the evidence that a local projection is complete; Kit only standardizes how that evidence reaches consumers.

Scope

This does not interpret product cursors, replica entities, or DTOs. It adds no persistence or state machine.

Validation

• focused offline request-policy tests: 7/7 passed
• Kit lint passed
• production Kit package build passed
• Kit full run: 46/47 files and 856 tests passed
• unrelated social-login spec timed out only under the full run; the same spec passed 18/18 in isolation
• Winecode consumer focused suite passed 8 files / 163 tests against the packed local build