[Frontend] Add browser back/refresh recovery for in-progress forms

## Problem
Long pet, medical-record, and appointment forms can lose user input or create duplicate submissions when navigation, refresh, or a wallet prompt interrupts the flow.

## Scope
Persist only non-sensitive draft fields, warn before destructive navigation, and reconcile drafts with server state after interruption.

## Acceptance criteria
- Draft persistence is scoped to the authenticated user and expires automatically.
- Secrets, medical attachments, and wallet signing payloads are never stored in browser storage.
- Refresh/back navigation restores a draft with a visible timestamp and discard action.
- Submit uses an idempotency key and clears the draft only after confirmed success.
- Tests cover refresh, back navigation, logout/login as another user, expiry, attachment interruption, and duplicate submit.

Start by mapping the pet, medical-record, and appointment form entry points and their current submit and navigation handling; the issue does not identify specific files or tests. Done means the listed interruption, user-isolation, expiry, attachment, and duplicate-submit cases are covered and drafts are cleared only after confirmed success.

Written by the indexing model from the issue text.