[Frontend] Add stale-data indicators and refresh policy to offline pet views

## Problem
Offline mode can show cached medical and emergency data without making its age or verification state obvious.

## Scope
Display last-synced/last-verified timestamps, stale thresholds by data type, and explicit refresh/retry states.

## Acceptance criteria
- Every offline-capable view identifies cached, syncing, current, and stale states.
- Emergency data shows age and verification status without exposing extra private data.
- Refresh actions are cancellable and do not overwrite newer local edits.
- Stale thresholds are centralized and documented.
- Tests cover no cache, fresh cache, stale cache, failed refresh, and clock skew.

Start by locating the offline-capable pet views, their cache and refresh handling, and the existing frontend test setup. Trace how cached medical and emergency data is represented, then add the documented states and thresholds while preserving local edits; done means the listed cache, refresh, privacy, clock-skew, and cancellation cases are covered by tests.

Written by the indexing model from the issue text.